Coal tar ointments have been used for many years in the treatment of chronic eczematoid dermatitis. The possible carcinogenic effect of coal tar ointment and ultraviolet light (Goeckerman regimen), considered individually or in combination, has been of concern to physicians. A 25-year follow-up study was completed on 426 patients with atopic dermatitis and neurodermatitis who were hospitalized and treated with coal tar ointments and ultraviolet light at the Mayo Clinic from 1950 through 1954. These results were compared with those from a similar study that examined patients with psoriasis who also were treated with coal tar ointments and ultraviolet light. The results of this study suggest that the incidence of skin cancer is not significantly increased above the expected incidence for selected populations of the United States. This study offers reassurance about the relatively small risk of skin cancer developing in patients with atopic dermatitis and neurodermatitis treated with coal tar ointments and ultraviolet light (Goeckerman regimen).