BACKGROUND: Veterans Affairs (VA) Cooperative Study 380 showed that some advan ced colorectal neoplasias (i.e., adenomas at least 1 cm in diameter, villous ade nomas, adenomas with highgrade dysplasia, or cancer) in men would be missed wi th the use of flexible sigmoidoscopy but detected by colonoscopy. In a tandem st udy, we examined the yield of screening colonoscopy in women. METHODS: To determ ine the prevalence and location of advanced neoplasia, we offered colonoscopy to consecutive asymptomatic women referred for coloncancer screening. The diagno stic yield of flexible sigmoidoscopy was calculated by estimating the proportion of patients with advanced neoplasia whose lesions would have been identified if they had undergone flexible sigmoidoscopy alone. Lesions were considered detect able by flexible sigmoidoscopy if they were in the distal colon or if they were in the proximal colon in patients who had concurrent small adenomas in the dista l colon, a finding that would have led to colonoscopy. The results were compared with the results from VA Cooperative Study 380 for agematched men and women wit h negative fecal occultblood tests and no family history of colon cancer. RESU LTS: Colonoscopy was complete in 1463 women, 230 of whom (15.7 percent) had a fa mily history of colon cancer. Colonoscopy revealed advanced neoplasia in 72 wome n (4.9 percent). If flexible sigmoidoscopy alone had been performed, advanced ne oplasia would have been detected in 1.7 percent of these women (25 of 1463) and missed in 3.2 percent (47 of 1463). Only 35.2 percent ofwomen with advanced neop lasia would have had their lesions identified if they had undergone flexible sig moidoscopy alone, as compared with 66.3 percent of matched men from VA Cooperati ve Study 380 (P< 0.001). CON CLUSIONS: Colonoscopy may be the preferred method of screening for colorectal cancer in women. BACKGROUND: Veterans Affairs (VA) Cooperative Study 380 showed that some advan ced colorectal neoplasias (ie, adenomas at least 1 cm in diameter, villous ade no nomas, adenomas with highgrade dysplasia, or cancer) in men would be missed wi th the use of flexible sigmoidoscopy but detected by colonoscopy. In a tandem st udy, we examined the yield of screening colonoscopy in women. METHODS: To determining ine the prevalence and location of advanced neoplasia, we offered colonoscopy to consecutive asymptomatic women referred for colon  cancer The diagno stic yield of flexible sigmoidoscopy was calculated by estimating the proportion of patients with advanced neoplasia whose lesions would have been identified if they had undergone flexible sigmoidoscopy alone. Lesions were considered detect able by flexible sigmoidoscopy if they were in the distal colon or if they were in the proximal colon in patients who had concurrent small adenomas in the dista l colon, a finding that would ha ve led to colonoscopy. The results were compared with the results from VA Cooperative Study 380 for age-matched men and women wit h negative fecal occult blood tests and no family history of colon cancer. RESU LTS: Colonoscopy was complete in 1463 women, 230 of Colonoscopy revealed advanced neoplasia in 72 wome n (4.9 percent). If flexible sigmoidoscopy alone had been performed, advanced neoplasia would have been detected in 1.7 percent of these women (25 of 1463) and missed in 3.2 percent (47 of 1463). Only 35.2 percent of women with advanced neop lasia would have had their lesions identified if they had undergone flexible sig moidoscopy alone, as compared with 66.3 percent of matched men from VA Cooperati ve Study 380 (P <0.001). CON CLUSIONS: Colonoscopy may be the preferred method of screening for colorectal cancer in women.