Using data from a national skin cancer survey, we assessed the risk of basal cell and squamous cell carcinoma among patients with psoriasis compared with the general population. For both male and female psoriatic patients, the risk of basal cell carcinoma was significantly elevated (relative risk = 2.2 and 1.7; p less than 0.05, both comparisons). The risk of squamous cell carcinoma was not significantly or substantially different for persons with a history of psoriasis compared with other persons (relative risk = 1.3; p greater than 0.05). The relative risk of basal cell skin cancer among patients with psoriasis was significantly higher even after stratification for factors associated with both psoriasis and cutaneous malignancy, which include fair complexion, exposure to coal tar or pitch, and exposure to radiation. Contrary to long-standing beliefs, our findings support the hypothesis that even after allowing for possible greater exposures to cutaneous carcinogens, the risk of nonmelanoma skin cancer in patients with psoriasis is at least as great as in the general population. Thus persons with psoriasis who are treated with potential carcinogens such as ultraviolet radiation, tar, and oral methoxsalen photochemotherapy merit careful, long-term monitoring.