OBJECTIVE To evaluate the efficacy of barium enema examination as routinely performed in the detection of colon cancer in the inhabitants of a well-defined and circumscribed geographic region. METHODS The study comprised 571 patients with histopathologically verified colon cancer during 1990-1993 from the county of Hordaland. The barium enema examination results were reviewed retrospectively. RESULTS The correct diagnosis was reached in 351 cases (sensitivity, 90.9%) in 386 tumor locations on the basis of the results of 381 barium enema examinations. Cancer or an important precancerous lesion was overlooked in 26 cases (6.7%), and the examination was not feasible in nine cases (2.3%). The correct diagnosis was reached in 172 cases (sensitivity, 80.0%) in patients with 215 tumor locations on the basis of the results of 213 colonoscopies. Cancer or an important precancerous lesion was overlooked in 13 cases (6.0%). The examination was technically not successful (i.e., the affected area was not reached with the scope) in 30 cases (13.9%). CONCLUSIONS Barium enema examination is valuable in the diagnosis of colon cancer and compares favorably with colonoscopy. The main reason for missed radiologic diagnosis is failure to observe important lesions visible on the radiographs.