Study published in JAMA, 1997; 277(13): 1052-1057. The objective was to assess the prevalence of circumcision across various social groups and examine the health and sexual outcomes of circumcision. The authors analyzed the National Health and Social Life Survey (NHSLS) data to determine the effects of circumcision. The results indicate, "We find no significant differences between circumcised and uncircumcised men in their likelihood of contracting sexually transmitted diseases." 

With respect to STDs, we found no evidence of a prophylactic role for circumcision and a slight tendency in the opposite direction. Indeed, the absence of a foreskin was significantly associated with contraction of bacterial STDs among men who have had many partners in their lifetimes. These results suggest a reexamination of the prevailing wisdom regarding the prophylactic effect of circumcision. While circumcision may have an impact that was not picked up by the NHSLS data, it seems unlikely to justify the claims made by those who base their support for widespread circumcision on it.