Because of the difficulty and expense of objectively measuring psoriasis severity, very little information exists on the severity of psoriasis in populations. We determined severity in a psoriasis patient population using the validated self-administered psoriasis area and severity index (SAPASI). This population consisted of 578 university dermatology clinic psoriasis patients, and data were analyzed from 317 (55%) questionnaire respondents. The majority of our sample was women (57%), and non-Caucasians represented a larger portion (8 %) in our sample compared with some previous studies. In our population, the reported frequencies of skin and joint symptoms were as follows: pruritus (95 %), skin burning (81 %), joint pain (69%), arthritis (51%), and psoriatic arthritis (20%). The SAPASI was significantly associated with severity of pruritus, burning, joint pain, and psoriatic arthritis. There was a significant negative correlation between the number of treatments employed and the SAPASI. This study provides results of a detailed measurement of the severity of psoriasis in a psoriasis patient population and relates this severity to population characteristics.