Eighty-two patients with pityriasis versicolor were treated orally with ketoconazole in tablet form (200 mg). The tablets were taken at least 90 min before a meal, and patients who received only one tablet daily were told to refrain from bathing except immediately before ingestion of the drug and only once a day. Dosage of ketoconazole varied from a single dose of 400 mg to 200–400 mg per day for four weeks. Seventy-seven patients reported no adverse effects. There were reports from others of headache, gastralgia, nausea, dyspnea, dizziness, or tinnitus. In most affected patients, these symptoms stopped with the first meal eaten after initiation of treatment. Follow-up examinations were performed at different intervals. The maximal therapeutic effect of ketoconazole was seen three to six weeks after initiation of therapy. Seventy-eight patients were considered cured; one had received only one tablet. Only hypopigmented macules remained. Examination of these areas with a Wood lamp revealed no fluorescence, and scrapings examined with the light microscope did not contain Malassezia furfur. These results indicate that ketoconazole is effective in the treatment of pityriasis versicolor, but the problem of protecting susceptible persons from infection and reinfection remains.