The risk for colorectal cancer in Crohn's disease and ulcerative colitis patients from the United States currently is unknown. We estimated the risk for small-bowel and colorectal cancer in a population-based cohort of 692 inflammatory bowel disease patients from Olmsted County, Minnesota, from 1940 to 2001. The Rochester Epidemiology Project was used to identify cohort patients with colorectal and small-bowel cancer. The cumulative probability of cancer and standardized incidence ratios (SIR) were estimated using expected rates from Surveillance, Epidemiology, and End Results, white patients from Iowa, from 1973 to 2000, and Olmsted County, from 1980 to 1999. Colorectal cancer was observed in 6 ulcerative colitis patients vs 5.38 expected (SIR, 1.1; 95% confidence interval [CI], 0.4-2.4), but 4 of these occurred among those with extensive colitis or pancolitis (SIR, 2.4; 95% CI, 0.6-6.0). Six Crohn's disease patients (vs 3.2 expected) developed colorectal cancer (SIR, 1.9; 95% CI, 0.7-4.1). Three Crohn's disease patients developed small-bowel cancer vs 0.07 expected (SIR, 40.6; 95% CI, 8.4-118). The risk for colorectal cancer was not increased among ulcerative colitis patients overall, but appeared to be increased among those with extensive colitis. The colorectal cancer risk was increased slightly among Crohn's disease patients, who also had a 40-fold excess risk for small-bowel cancer.