To study the relationship between possible predictive factors such as the microcystic character of acne, endocrinological disorders, dosing schedule, and the occurrence of either early or late relapses, 237 patients (mostly females) were treated with daily dosages according to clinical and biological tolerance. Duration of the treatment ensured whenever possible an efficient total cumulative dose. Acne was graded initially, at the end of the treatment and one year thereafter. Failure was defined as the persistence or the occurrence of inflammatory lesions graded at 2 or more. Complete clearing at the end of treatment was observed in 218 patients. Correlations between clearing and age, sex or endocrinological disorders could not be established. Patients with microcystic acne cleared less. Failures have been recorded in 120 patients. Relapses were more frequent in patients with microcystic acne or endocrinological disorders as well as in those with high graded acnes on the face, on the back and on the chest. No relationship was found between total or daily dose and occurrence of failures. Definitive clearing was more frequent in patients who received a total cumulative dose between 75 and 150 mg/kg. These long term results in a cohort of acne patients treated with isotretinoin justify a reappraisal of the treatment strategy.