In epidemiologic studies of the relation between circumcision and sexually transmitted infections, it is necessary to rely on self-report of circumcision status. The purpose of this 2002 study in Houston, Texas, was to determine whether adolescent males could make correct self-reports. During physical examinations, adolescents were asked whether they were circumcised. The authors then examined the adolescents’ genitalia. Circumcision status was recorded as complete (glans penis fully exposed), partial (glans partly covered), or uncircumcised (glans completely covered). The mean age of the 1,508 subjects was 15.0 (standard deviation, 1.63) years; 64% were Black, 29% Hispanic, and 7% White. Forty-nine percent had full, 1% partial, and 50% no circumcision. Of the 738 fully circumcised subjects, 512 (69%) considered themselves circumcised, 54 (7%) considered themselves uncircumcised, and 172 (23%) did not know. Of the 751 uncircumcised youth, 491 (65%) described themselves as uncircumcised, 27 (4%) reported being circumcised, and 233 (31%) did not know. The sensitivity of self-report among those who thought they knew their status was 90.5%, and the specificity was 94.8%; 27% did not know their status. In this population, self-report of circumcision status did not result in accurate information mainly because many adolescents were unsure of their status.