To explore attitudes toward circumcision among men who have sex with men (MSM) in London and the feasibility of conducting research into circumcision and HIV prevention in this population. A convenience sample of MSM visiting central London gyms completed a confidential, self-administered questionnaire between May and June 2008. Information was collected on participants' demographic characteristics, self-reported HIV status, sexual behavior, circumcision status, attitudes toward circumcision, and willingness to participate in research on circumcision and HIV prevention. Of 653 MSM, 29.0% reported that they were circumcised. Overall, HIV prevalence was 23.3%; this did not differ significantly between circumcised and uncircumcised men (18.6% vs. 25.2%, respectively; adjusted odds ratio 0.79, 95% confidence interval: 0.50-1.26). A similar proportion of circumcised and uncircumcised men reported unprotected anal intercourse in the previous 3 months (38.8% vs. 36.7%, adjusted odds ratio 1.06, 95% confidence interval: 0.72-1.55). Uncircumcised men were less likely to think that there were benefits of circumcision than circumcised men (31.2% vs. 65.4, P < 0.001). Only 10.3% of uncircumcised men said that they would be willing to participate in research on circumcision as an HIV prevention strategy. Most uncircumcised MSM in this London survey were unwilling to participate in research on circumcision and HIV prevention. Only a minority of uncircumcised men thought that there were benefits of circumcision. It is unlikely that circumcision would be a feasible strategy for HIV prevention among MSM in London.