Since our preliminary report of psoralen plus long-wave ultraviolet A (PUVA) therapy in ten patients with erythroderma-type or plaque-type mycosis fungoides (MF), we have treated 38 patients with biopsy-proved MF. Approximately one third, mostly patients with erythroderma, received PUVA as primary therapy; the remainder had recurrent disease following electron beam irradiation or topical mechlorethamine (Mustargen) hydrochloride. Follow-up data are presented in 29 patients who completed an initial course of PUVA given two to three times weekly. A complete clinical response was observed in ten patients with plaque-type MF and seven with erythroderma without Sézary syndrome. The PUVA therapy was palliative for patients with advanced disease, in combination with other therapies. The mean observation period was approximately five years. Despite maintenance PUVA, most patients relapsed between ten and twenty months and were treated with another intensive course. Long-term maintenance therapy with PUVA was necessary to control the disease.