The natural history of psoriasis was studied through a questionnaire survey of 5,600 patients throughout the United States. The mean age of onset of psoriasis was 27.8 years. 36% of the respondents reported familial occurrence of the disease. At the time of study, the lower extremities were indicated as being the most often affected; trunk, elbow, and scalp were next, knee and face were cited less frequently. Fingernails were involved in half of the patients at some time during the period of their disease. In the majority of patients, hot weather and sunlight had a beneficial effect. One third of the females also indicated improvement during the course of pregnancy. Remissions were reported in 39% of the patients.