Fifty consecutive patients with ulcerative colitis were personally examined to determine the lifetime prevalence of specific psychiatric diagnoses. A personality assessment and a tabulation of recently occurring stressful events were done. A matched control sample with chronic nongastrointestinal medical illnesses was evaluated in the same way. The two groups were compared so as to quantify the relative association and impact of psychiatric disorder in ulcerative colitis. We found no greater frequency of diagnosable psychiatric disorder in ulcerative colitis patients than in the control population. Those with ulcerative colitis and a psychiatric illness did not appear to have more serious gastrointestinal involvement, nor did severity of the ulcerative colitis predict more frequent or more serious psychiatric disorder. Personality profiles were similar in probands and controls, and there was no correlation between the frequency of potentially stressful life events within the six months prior to interview and severity of ulcerative colitis at the time of interview. We did find slightly higher levels of obsessional symptomatology in ulcerative colitis cases, but this association appeared to be weak and unrelated to the severity of the gastrointestinal disorder. Despite the fact that more than a quarter of the ulcerative colitis patients had some diagnosable psychiatric illness, the occurrence of psychiatric disorder was rarely documented in the medical charts.