['Seventy percent of patients with primary sclerosing cholangitis (PSC) have concomitant ulcerative colitis. Smoking and previous appendectomy may protect against ulcerative colitis. The aim of this study was to examine these factors in patients with PSC.', 'Fifty-nine patients with PSC, 130 patients with ulcerative colitis and normal liver biochemistry, and 197 control subjects were interviewed about smoking behavior and history of appendectomy.', 'There were less current smokers in the PSC and ulcerative colitis groups than in the control group (19%, 12%, and 38%, respectively). The resulting odds ratio for current smoking was 0.37 (95% confidence interval, (0.18-0.76) in the PSC group and 0.23 (95% confidence interval, 0.13-0.41) in the ulcerative colitis group. Percentage of persons who ever smoked was also significantly less in the PSC group (41% vs. 56% in the control group). Frequency of previous appendectomy in the PSC and ulcerative colitis groups was not significantly different from that of controls (19%, 9%, and 14%, respectively).'] Is risk of primary sclerosing cholangitis associated with nonsmoking behavior?