It's impossible to know exactly how many guest and impromptu performances The Waterboys have given but with a lot of help from Mike and Steve, here is a record of many of them.
   
May 1982 With Nikki Sudden, The Venue, London, England (Mike and Anto)
  Mike : Lead Gtr, Anto : Sax, whole set
 .

Dec 1982

With U2, Irish Tour (Steve)
 .
1983 With U2, Pheonix Park, Ireland (Steve)
   
July 1984 With Bob Dylan, Slane, Ireland (S)
  Song : "Leopard Skin Pillbox Hat"*
   
1985 With REM, SFX Centre, Dublin, Ireland (S)
  Song : Unknown
   
Jan 10 1986 With The Burglars, Cullen's Bar, Dublin (S and A)
  Songs : Unknown
   
Jan 19 1986 Unknown Benefit Show, Olympic Ballroom, Dublin (M and S)
  Songs : "Blowin In The Wind"* and others
   
Feb 14 1986 With Steve Cooney & Friends, Onion Field, Dublin (M, S, A)
  Songs : "Sweet Thing"*
"Girl From The North Country"*
"I Threw It All Away"*
"Belltable Waltz"*
"I'm So Lonesome I Could Cry"*
"Wayward Wind"*
"Death Is Not The End"*
"Fisherman's Blues" and others
   
Feb/Mar 1986 With The Pleasure Cell, The Underground, Dublin (M)
  Song : "Be My Enemy"
   
June 6 1986 Unknown Folk Club, Glasgow, Scotland (M, S, A)
  Songs : "Meet Me At The Station"*
"Belltable Waltz"* and others
   
Oct 1986 With Hennigan's Blues Band, Hennigan's Blues Bar, Sligo, Ireland (M)
  Song : "Lost Highway"*
   
  With We Free Kings, Blue Lagoon, Sligo (S)
  Songs : "Raggle Taggle Gypsy"* and others
   
  With We Free Kings, unknown venue, Cork, Ireland (M and S)
  Song : "Fisherman's Blues"
   
  With We Free Kings, Baggot Inn, Dublin (M and S)
  Songs : "My Generation"* and others
   
Nov 1986 With Fleadh Cowboys, Million Miles of Peace benefit concert, Dublin (M, S and A)
  Songs : "Forever Young"* plus one other
   
Dec 1986 With various Hothouse Flowers, The Waterfront Club, Dublin (M)
  Song : "When Will We Be Married ?"*
   
April 2 1987 With We Free Kings and other, Assembly Rooms, Edinburgh, Scotland (M and S)
  Songs : "My Generation"* "Will The Circle Be Unbroken"* and others
   
May 24 1987 With We Free Kings, Pictish Festival, Letham, Scotland (S)
  Songs : Whole set
   
May 31 1987 With various Fleadh Cowboys, Pogues and Liam O'Maonlai, Town Square, Kenmare Festival, Kenmare, Ireland (M and A)
  Songs : "On My Way To Heaven"*
"Maggie's Farm"*
"Can't Feel At Home In This World Anymore"*
"Girl From The North Country"*
"Cock In My Pocket"*
"Lost Highway"*
   
Aug 21 1987 With Fleadh Cowboys, Olympia Theatre, Dublin (M, S, A & Trevor)
  Songs : "On My Way To Heaven"*
"Has Anybody Here Seen Hank ?"
"Killing My Heart"
"Heading Down The Highway"
   
Sept 1987 With Fleadh Cowboys, Olympia Theatre, Dublin (M and T)
  Songs : "Rainy Day Women Nos 12 & 35"* and others
   
Sept 19 1987 With unknown country'n'western duo, Hibernian Bar, Galway, Ireland (M)
  Songs : "Honky Tonkin'"*
"Lost Highway"*
   
Sept 1987 With Vinnie Kilduff and Jean-Paul Huellou, Secondary School, Clifden, Co. Galway, Ireland (M)
  Songs : "Fisherman's Blues"
"Headin Down The Highway"
"The Whole Of The Moon" and one other
   
Sept 1997 With Chris Meehan And His Redneck Friends, unknown venue, Clifden (M)
  Song : "On My Way To Heaven"*
   
Oct 1987 With Hothouse Flowers, The Factory, Dublin (M, S and A)
  Songs : "Cock In My Pocket"* and others
   
Nov 1987 With The Black Velvet Band, The Waterfront, Dublin (M, S and A)
  Song : unknown
   
Jan 1988 Jimmy Hickey's wedding reception, Dublin (M, S , A and T)
  Songs : "Black Is The Colour"*
"Fisherman's Blues" and others
   
Feb 1988 With Fleadh Cowboys, The Castle, Salthill, Galway (M and T)
  Songs : "Roll Over Beethoven"* and one other
   
April/May 1988 With The Sawdoctors, Claddagh Hall, Galway (M and S)
  Song : "Streets Of Galway"*
   
August 1988 With Hothouse Flowers, RDS, Dublin (S)
  Song : "Dance To The Storm" (HHF Song)
   
Sept 1988 With Hank Halfhead And The Rambling Turkeys, Bad Bob's, Dublin (M)
  Song : "Lost Highway"*
   
Dec 13 1988 With various Dublin bands/musicians, Christmas Benefit Concert, Olympia Theatre, Dublin (M and T)
  Song : "Meet Me At The Station"*
   
March 1989 With The Sawdoctors, Hermitage Hotel, Tuam, Ireland (M)
  Songs : "Rainy Day Women Nos 12 & 25"* and others
   
May 1989 With local musicians, The Kitchen, Carraroe, Connemara, Ireland (M)
  Song : "Can't Help Falling In Love"*
   
July 29 1989 With Sharon Shannon, The Taibhearc Theatre, Galway (M, S and T)
  Songs : "In Search Of A Rose"
"Song For The Life"* and many tunes
   
July 30 1989 With The Sawdoctors, Warwick Hotel, Galway (M)
  Songs : "Lost Highway"*
"This Land Is Your Land"*
   
August 1989 With Cooney and Begley, unknown venue, Killarney, Ireland (M)
  Songs : "Lost Highway"* and one other
   
April/May 1990 With The Sawdoctors, Seapoint, Galway (M)
  Songs : "Garageland"*
"Back In The USSR"* and lead guitar on whole Sawdoctors set
   
August 1990 With Christy Moore, The Feile, Tipperary, Ireland (S)
  Songs : "Raggle Taggle Gypsy"*
"The Inchicore Reel"
   
Feb 1991 With Charlie Lennon and Dublin musicians, Olympia Theatre, Dublin (M)
  Songs : "When Ye Go Away"
"Ride On"*
   
August 1991 With The Sawdoctors, The Feile, Tipperary, Ireland (M)
  Songs : "And A Bang On The Ear"
"The Trip To Tipp"
   
Sept 7 1991 With Various Sawdoctors and a cabaret band, Imperial Hotel, Tuam (M and T)
  Songs : "And A Bang On The Ear"
"Fields Of Athenry"*
"At The Hop"*
"Satisfaction"* and others
   
Late 91/Early 92 With The Sawdoctors, Tramps, New York, USA (M)
  Songs : "Drive Away"*
"Pretty Vacant"*
   
October 1992 With various Scottish musicians, Open World night, .........Glasgow (M)
  Songs: "I'll Be Your Baby Tonight"*
"On My Way To Heaven"*
"Buckets Of Rain"*
   
March 1993 With Pal Shazar, unknown venue, South By Southwest, Austin, USA (M)
  Song : "Wade Went Wild" (Pal's song)
   
April 1993 With Victoria Williams, Tramps, New York (M)
  Song : "Why Look At The Moon"*
   
May 1993 Cafe Sin E, East Village, New York (M)
  Song : "Send Him Down To Waco"
   
Jan 21 1994 Universal Hall, Findhorn, Scotland (M)
  Song : "Mother Cluny"
   
March 1994 Universal Hall, Findhorn (M)
  Song : "LCG Song" and whole set backing singer Nicky Robertson
   
April 6 1994 Universal Hall, Findhorn (M)
  Song : "What Do You Want Me To Do ?"
   
May 1994 With Tinderbox, unknown venue, Elgin, Scotland (M)
  Songs : "Medicine Bow"
"Be My Enemy"
"All Along The Watchtower"*
   
June 1994 Universal Hall, Findhorn (M)
  Song : "Forever Young" and songs backing singer Diana Herbst
   
  With Ian McNabb, Glastonbury Festival, England (M)
  Songs : "Glastonbury Song"
"Preparing To Fly"
   
  With Sharon Shannon, Glastonbury Festival (M)
  Songs : "When Ye Go Away"
"Song For The Life"*
   
July 1994 Backing Julia, Universal Hall, Findhorn (M)
  Song : "Sarajevo Women's Anthem"
   
August 1994 Steiner School Benefit, Universal Hall, Findhorn (M)
  Songs : "Bring 'Em All In"
"Wonderful Disguise"
"Experience Week Song"
   
Nov 17 1994 Universal Hall, Findhorn (M)
  Songs : "The Return Of Pan"
"Long Way To The Light"
   
Dec 1994 With Jazz Band, Universal Hall, Findhorn (M)
  Songs : "Accentuate The Positive"*
"Rudolf The Red Nosed Reindeer"
   
January 1995 With Jazz Band, Universal Hall, Findhorn (M)
  Songs : "It Ain't What You Do"*
"Universal Hall"
   
1996 With Luka Bloom, Frankie Gavin, Mairtin O'Connor, Greenpeace Benefit show, Athlone, Ireland (S)
  Songs : "You Couldn't Have Come At A Better Time"(Luka Bloom) Various traditional tunes
   
Dec 18 1999 Pulkvedian Neviens Neraksta, Riga, Latvia (M)
  Song : "Bring 'Em All In"
   
Jan 16 2000 With Carlos Nunez, National Concert Hall, Glasgow (M)
  Songs : "Raggle Taggle Gypsy"* "Fisherman's Blues"