Predictors of the radiologic detection of colorectal polyps or cancer were studied in 1852 patients referred from primary health care for a double-contrast barium enema. Significant polyp predictors were age 40-79 years (odds ratio (OR), 2.4-5.0) and rectal bleeding (OR, 1.8). Previous colorectal neoplasm, familial history of cancer in general, and male sex were nearly significant predictors of polyps. Significant cancer predictors were age > or = 60 years (OR, 8.6-27.8), rectal bleeding (OR, 2.7), loss of weight (OR, 2.6), and male sex (OR, 2.2). Fatigue and abdominal pain were nearly significant negative predictors for cancer. No association was found between patient delay and the detection of polyps or cancer. Physician delay was significantly shorter in patients with cancer than in cancer-free patients. Age was the most important predictor for the detection of both polyps and cancer, more important than symptoms and history, including family history.