The purposes of our study were to 1) identify the number of neoplastic lesions (adenomatous polyps and cancer) diagnosable by flexible sigmoidoscopy (FS) in patients with symptoms of colorectal disease and 2) determine the age distribution of patients in whom neoplastic lesions are detected by FS. A total of 1015 patients, ages 20-89 years, underwent FS because of the following indications: rectal bleeding, occult blood loss, anemia, change in bowel habit, weight loss, and abdominal pain. FS examined a mean distance of 49 +/- 2 cm (SEM) in an average time of 11.5 min. A bowel preparation of 2 Fleet enemas was adequate in 95% of patients and the examination was well tolerated by all age groups. There were no complications encountered. Eight-five neoplastic lesions were identified in 78 patients. Fifty-four percent of all adenomatous polyps and 61% of the cancers were detected beyond 20 cm. Neoplastic lesions were identified in all adult decades studied, ranging from 3.2% of patients aged 20-40 years, 8.0% for patients between 40 and 60, and 10.1% from 60 to 80; with a peak yield of 11.2% in the 7th decade. Cancer was diagnosed only in patients more than 40 years; 3.3% of patients over 60 had carcinoma compared to 0.8% in patients less than 60. These data provide evidence for the value of FS as a safe initial diagnostic procedure to detect neoplastic lesions in symptomatic patients of all adult age groups.