125cc Grand Prix leading entries for 1991:
| no. | rider | entrant | bike |
| 1 | Loris Capirossi ITA | AGV-Pileri Corse | Honda RS |
| 7 | Fausto Gresini ITA | AGV-Pileri Corse | Honda RS |
| 2 | Hans Spaan NED | Sharp Samson Racing Team | Honda RS |
| 46 | Arie Molenaar NED | Sharp Samson Racing Team | Honda RS |
| 3 | Bruno Casanova ITA | Team Semprucci IDM | Honda RS |
| 4 | Dirk Raudies BRD | Schuh HB Honda Racing Team | Honda RS |
| 5 | Jorge Martínez ESP | Elf Coronas Racing Team | JJ Cobas-H’a |
| 14 | Julián Miralles ESP | Elf Coronas Racing Team | JJ Cobas-H’a |
| ? | Jaime Mariano ESP* | Elf Coronas Racing Team | JJ Cobas-H’a |
| 5 | Jorge Martínez ESP | Metraux | Honda RS |
| 6 | Ezio Gianola ITA | Derbi Racing Team | Derbi |
| 66 | Luis I Alvaro ESP# | Derbi Racing Team | Derbi |
| 9 | Alessandro Gramigni ITA | Team Italia | Aprilia |
| 12 | Gabriele Debbia ITA | Team Italia | Aprilia |
| 10 | Heinz Lüthi SUI | Elf Competition | Honda RS |
| 11 | Adolf Stadler BRD | RS Rallye Sport GmbH | JJ Cobas |
| 15 | Maurizio Vitali ITA | Gazzaniga Corse | Gazzaniga |
| 34 | Emilio Cuppini ITA | Gazzaniga Corse | Gazzaniga |
| 16 | Koji Takada JAP | Team Takeshima | Honda RS |
| 17 | Steve Patrickson ENG | Derek Clarke Racing Team/Levior | Honda RS |
| 18 | Robin Appleyard ENG | Colin Appleyard Racing | Honda RS |
| 19 | Alfred Waibel BRD | ? | Honda RS |
| 20 | Hisashi Unemoto JAP | Team Unemoto | Honda RS |
| 22 | Peter Öttl BRD | AGV Racing Team | Rotax |
| 63 | Stefan Kurfiss BRD# | AGV/MDS Racing Team | Rotax |
| 26 | Javier F Debón ESP | JJ Cobas Ducados-Agrati | Honda RS |
| 27 | Gimmi Bosio ITA | HB Italy/Gilera Club | Honda RS |
| 28 | Ralf Waldmann BRD | Schuh/Zwafink Honda Racing | Honda RS |
| 29 | Peter Galvin AUS | Team Driza Bone | Honda RS |
| 35 | Kazuto Sakata JAP | Team Elf Kepla/Meiko | Honda RS |
| 36 | Ian McConnachie ENG# | Clay Cross Motorcycles | Honda RS |
| 39 | Johnny Wickström FIN# | Silja Line Racing Team | Honda RS |
| 41 | Alain Bronec FRA | Ville de Thiers | Honda RS |
| 42 | Herri Torrontégui ESP | Herri Racing Team | JJ Cobas |
| 44 | Javier Torrontégui ESP**# | Herri Racing Team | JJ Cobas |
| 43 | Manuel Hernández ESP | Racing Team Honda Cartagena | Honda RS |
| 45 | Thierry Feuz SUI | BP Racing Team Switzerland | Honda RS |
| 47 | Olivier Petrucciani SUI# | Marlboro Aprilia Mohag | Aprilia |
| 49 | René Dünki SUI | Dianetik Racing Team | Honda RS |
| 50 | Hubert Abold BRD | Moto Co Team Kepla | Honda RS |
| 50 | Antonio Sánchez ESP**# | Team Ducados | JJ Cobas |
| 53 | Carlos Giró ESP**# | Team Ducados | JJ Cobas |
| 51 | Nobuyuki Wakai JAP# | Moto Bum Racing Team | Honda RS |
| 53 | Akira Saitoh JAP** | ? | Honda RS |
| 54 | Soichiro Sato JAP** | ? | Honda RS |
| 55 | Masato Shima JAP** | ? | Honda RS |
| 55 | Jos van Dongen NED# | Ringleberg Team | Honda RS |
| 56 | Noboru Ueda JAP# | Hero Sports TS | Honda RS |
| 58 | Kinya Wada JAP# | ICM Racing Associates | Honda RS |
| 61 | Serafino Foti ITA# | Eugenio Lazzarini Racing | Honda RS |
| 62 | Stefan Brägger SUI | Team Brägger | Honda RS |
* replacement rider
** wildcard rider at selected events
# Alvaro also raced number 62
# Kurfiss also raced number 57
# McConnachie also raced numbers 45 and 62
# Wickström also raced numbers 51 and 40
# Torrontégui also raced number 40
# Petrucciani also raced numbers 48 and 76
# Sánchez also raced numbers 61 and 75
# Giró also raced numbers 60 and 76
# Wakai also raced numbers 52, 61, 36 and 39
# van Dongen also raced numbers 52 and 71
# Ueda also raced numbers 60, 36, 30 and 37
# Wada also raced numbers 73, 60, 33 and 43
# Foti also raced number 38
With grateful thanks to Phil Wain of RealRoadRacing.com
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