The development in 1974 of psoralen photochemotherapy (PUVA) for severe psoriasis transformed the therapeutic setting for this disease from in-patient to ambulatory, presaging the trend in the past decade to reduce hospitalization. The prospective evaluation of this treatment in well-designed, well-controlled studies with the participation of a large cohort of patients, which expanded for 12 years and involved prestigious academic centers in the United States and Europe, is one of the largest medical enterprises ever conducted and is a testament to scientific investigation and collaboration. Besides its contribution to mitigating the suffering of patients with this disease, the intense scientific pursuit by so many investigators has contributed significantly to the understanding of photomedicine, especially photochemical and photobiologic reactions, and to its place in the clinical arena and in the forefront of dermatologic interest. This article is an account of this scientific endeavor, which now enters its third decade, as well as a recognition of its contributors.