Patients with a primary family history of colon cancer were recommended to have full colonoscopy for screening. The results of 125 such patients who also were asymptomatic, had no prior history of neoplasms, and had negative fecal occult blood, showed 15 patients (12 percent) with neoplasms. Only 6 (5.2 percent) had neoplasms that were detectable only by colonoscopy (i.e., above 55 cm). These results suggest that colonoscopy may not be necessary to screen patients with a primary history of colon cancer.