89 patients (66 males and 23 females) with severe acne were treated with isotretinoin and were followed up for a period of 6-47 months (mean 14 months) after the end of the therapy. Relapses occurred in 14.6% of the patients. They were not found to be related to the total amount of isotretinoin administered (up to 233 mg/kg); a possible, although not significant, link to sex was observed since relapses occurred in 16.6% males and 8.6% of females. But the age of the patients had a significant bearing on the likelihood of relapses: younger patients relapsed more frequently than older patients.