Extensive psoriasis in 1,308 patients has been treated two or three times a week with oral 8-methoxypsoralen followed by high intensity, long-wave ultraviolet light (PUVA). Excluding 169 patients still under early treatment, psoriasis cleared in 88% and failed to clear in 3%. One percent dropped out due to complications of treatment, and 8% for other reasons. The twice-a-week schedule was superior for patients with lighter skin types. Once a remission was induced, there was no difference in its maintenance when patients were treated once a week, once every other week, or once every third week. Each of these schedules was superior to no maintenance treatment. Immediate side effects of the 45,000 treatments administered in the first 18 months of this study were uncommon, temporary, and generally mild. No clinically significant changes in laboratory screening or eye examinations attributable to PUVA have been uncovered.