Thirty patients with treatment-resistant cystic and conglobulate acne entered a randomized double-blind protocol, testing the efficacy of isotretinoin versus tetracycline. After 16 weeks of isotretinoin treatment, the mean number of cysts decreased by 64% and the mean sum of the longest diameters was reduced by 68%. After 16 weeks of tetracycline therapy, the total number of cysts showed a mean decrease of 52%, and the mean sum of the longest diameters decreased by 60%. The reduction in the number of cysts and the sum of their longest diameters that occurred after 16 weeks of treatment was statistically significant for each of the treatment groups, but there was no statistically significant difference between the treatment groups at the end of therapy. Eight weeks after the discontinuation of treatment in the isotretinoin group, there was an overall reduction from baseline of 82% in the cyst count and 88% in the sum of the longest diameters. In the tetracycline treatment group, the overall reduction from baseline in the cyst count was 54% and in the sum of the longest diameters, 60%. This led to a statistically significant difference in the two treatment groups at 24 weeks. All patients on isotretinoin experienced side effects that were primarily related to the integumentary system but necessitated discontinuation of the drug for a short period of time in only one patient. Long-term follow-up, 8 months after discontinuation of the study, showed a prolonged significant remission of acne in the isotretinoin group but not in the tetracycline group.