There was no change to the entry at Monaco and no change on pole position with Ayrton Senna fastest in his McLaren-Honda. There was a surprise in second place with the Pirelli-shod Tyrrell-Honda of Stefano Modena ahead of Riccardo Patrese's Williams-Renault, Nelson Piquet's Benetton-Ford, Nigel Mansell (Williams), Gerhard Berger (McLaren) and the Ferrari of Alain Prost. The top 10 was rounded off by the Benetton of Roberto Moreno, Jean Alési's Ferrari and Andrea de Cesaris in his Jordan.

Modena made a good start but Senna took the lead with Modena second ahead of Patrese, Mansell and Prost. Berger ran into Piquet at the first corner and Piquet was out. Berger would disappear soon afterwards. After stopping for repairs he was charging back when he hit the wall in the Swimming Pool area while trying to wipe his visor. Modena suffered badly from traffic and so fell back to Patrese. Pierluigi Martini was the cause and he became the first man in F1 history to get a 10-second stop/go penalty penalty, which meant going into the pits and waiting 10 seconds before being allowed back onto the track.

On lap 30 Prost overtook Mansell for fourth place but otherwise the order was stable until lap 43 when Modena's engine blew up in the tunnel. Patrese hit the oil and spun wildly. This left Senna with a huge advantage over Prost with Mansell, his engine problem suddenly curing itself, beginning to charge. Alési continued his lonely race in fourth and Moreno did the same in fifth.

On lap 63 Mansell dived ahead of Prost with a wild manoeuvre but Prost was smart enough to keep out of the way of the errant Williams. Prost's race was ruined when he had to pit to have a wheel tightened and so he finished fifth behind Senna, Mansell, Alési and Moreno. J.J. Lehto lost sixth when his Dallara's gearbox failed but there was some consolation as his team mate Emanuele Pirro took the final point.

Senna had scored four wins in four races.