I read with great interest the recent paper by Crosby et al., in which the authors failed to find any significant difference in the prevalence of HIV (or other sexually transmitted infections) between circumcised and intact young black men who have sex with men (MSM) in the United States [1]. Their findings are in line with those of a 2011 Cochrane review showing no significant association overall between circumcision/foreskin status and HIV infection in MSM, although a subanalysis suggested a possible reduction in HIV risk among circumcised MSM who predominantly take the insertive role during anal sex [2]. However, a subsequent British study found no evidence that circumcision is protective against HIV among MSM who predominantly engage in anal sex as the insertive partner [3]. Crosby et al. highlight an additional, potentially noteworthy finding in their article’s abstract [1]. They report that ‘‘The mean frequency of unprotected insertive anal sex for circumcised men was about twice as high compared to those intact (P = .04).’’ This finding is consistent with evidence from another recent study by Feldblum et al. [4], which pointed to reduced condom use following adult circumcision among a large sample of Kenyan men. Unfortunately, Crosby et al. make no mention anywhere in the main text about this statistically significant finding. Perhaps the authors considered it to be a chance finding because, apparently, it was the only statistically significant result in their study. However, there are reasons why this finding may actually deserve some attention. First, such a result is plausible on anatomical and behavioral grounds. Since circumcision removes the adult equivalent of approximately 50 cm of touch-sensitive tissue (see below), one might expect an overall reduction in penile sensitivity as a function of the surgery. Since condoms tend to decrease penile sensitivity [5], circumcised men may have conscious or unconscious motivations to avoid any further desensitization during sex, which could explain their reduced condom use. Laboratory investigations have sought to determine whether the foreskin is a particularly sensitive penile structure, and have produced conflicting results. Some researchers have provided evidence that the foreskin is the most sensitive part of the penis [6], while others fail to confirm such findings [7]. However, regardless of whether sensitivity per square centimeter is actually higher in the foreskin compared to other parts of the penis, or the foreskin is merely as sensitive as other parts of the sexual organ, the overall sensory input from a circumcised penis during sex will be reduced in a manner that plausibly depends—at least to some extent—on the amount of foreskin removed. The obvious reason for this is that any sensation that would be experienced in the foreskin itself is necessarily eliminated by circumcision [8]. The adult foreskin—with its rich supply of nerve endings and specialized sensory structures [9]—may comprise up to 100 cm, with reported average values between 30 and 50 cm [10, 11]. The contribution of this motile sleeve of erogenous tissue to overall penile sensitivity is not known with certainty. However, any specific qualitative sensation elicited by the mechanical rolling and gliding movements of the foreskin during sexual activity will in fact be absent or reduced in circumcised men [8]. & Morten Frisch mfr@ssi.dk