Circumcision's potential link to HIV/sexually transmitted infections (STI) has been at the center of recent global public health debates. However, data related to circumcision and sexual health remain limited, with most research focused on heterosexual men. This study sought to assess behavioral differences among a large sample of circumcised and noncircumcised men who have sex with men (MSM) in the United States. Data were collected from 26,257 U.S. MSM through an online survey. Measures included circumcision status, health indicators, HIV/STI screening and diagnosis, sexual behaviors, and condom use. Bivariate and regression analyses were conducted to determine differences between HIV/STI status, sexual behaviors, and condom use among circumcised and noncircumcised men. Circumcision status did not significantly predict HIV testing (p > 0.05), or HIV serostatus (p > 0.05), and there were no significant differences based on circumcision status for most STI diagnosis [syphilis, gonorrhea, chlamydia, human papilloma virus (HPV)]. Being noncircumcised was predictive of herpes-2 diagnosis, however, condom use mediated this relationship. These data provide one of the first large national assessments of circumcision among MSM. While being noncircumcised did not increase the likelihood of HIV and most STI infections, results indicated that circumcision was associated with higher rates of condom use, suggesting that those who promote condoms among MSM may need to better understand condom-related behaviors and attitudes among noncircumcised men to enhance the extent to which they are willing to use condoms consistently.