Joint complaints of 1285 patients treated for cutaneous psoriasis were analyzed to better define the epidemiology of arthritis among psoriasis patients selected on the basis of cutaneous rather than rheumatologic disease. Nearly 40% of patients suffered from arthralgia, and 20% had been diagnosed as having psoriatic arthritis (PA). Patients with PA had more extensive cutaneous disease and more frequently had a family history of PA. PA patients frequently noted an association between the activity of their arthritis and the activity of their cutaneous disease. Antinuclear antibodies, uric acid, and white blood cell count had little predictive value in PA.