Although some discordance between sexual identity and sexual behavior is to be expected in any population and has been described in the context of nonrandom samples (13, 16, 18), our analysis suggests a larger discrepancy than has been noted previously in population-based studies. The Urban Men's Health Study (UMHS) (25) included a large probability sample of men who have sex with men, of whom only 3% perceived themselves as heterosexual. The UMHS, however, included households in neighborhoods known to be predominantly gay and probably does not provide an accurate measure of sexual identity among all men from the general population who have sex with men. Data from representative samples suggest that approximately 98% of men and women describe their sexual identity as heterosexual. The remaining 2% describe themselves as bisexual, homosexual, or undecided; however, substantially more than 2% report same-sex attraction, same-sex experience, or both (11). In their landmark population-based surveys of sexual behavior, Laumann and colleagues (12) found that although 9% of 18- to 59-year old men living in the largest U.S. cities identified as gay or bisexual in 1 study, a higher proportion of men (14.3%) surveyed in the same cities reported having male sexual partners in the past 5 years, 10.2% in the previous year. We report more marked differences using a single sample: In New York City, among sexually active men who also reported a sexual identity, 4% reported a gay identity but 12% reported same-sex sexual behavior in the past year. Despite the differences in phrasing of the question regarding sexual partners, the 2003 estimate of same-sex behavior in men was similar to that in the 2002 CHS.