| Champ: | Andrei Chesnokov |
| Runner: |  Thomas Muster |
| Score: | 7–5, 6–3, 6–3 |
| Draw: | 56 (6 / 4) |
| Seeds: | 16 |
| Type: | singles doubles |
See main article: 1990 Monte Carlo Open.
Andrei Chesnokov defeated Thomas Muster in the final, 7–5, 6–3, 6–3 to win the singles tennis title at the 1990 Monte Carlo Open.
Alberto Mancini was the defending champion, but lost in the second round to Henri Leconte.
The top eight seeds received a bye to the second round.
Stefan Edberg (third round)
Aaron Krickstein (second round) Jay Berger (second round)
Andrés Gómez (third round)
Emilio Sánchez (semifinals)
Martín Jaite (second round) Jim Courier (third round) Alberto Mancini (second round) Guillermo Pérez Roldán (second round) Horst Skoff (quarterfinals) Magnus Gustafsson (first round) Sergi Bruguera (second round)