Nearly 10 percent of self-identified straight men reported having sex with at least one man in the past 12 months, a New York City Department of Health and Mental Hygiene survey of 4,193 men found.
Almost 70 percent of the men who said they had sex with men were married. Many admitted to not using protection.
"Doctors need to ask patients about specific sexual practices instead of relying on self-reported sexual orientation to assess risk for unsafe sexual practices and risk for sexually transmitted diseases," Preeti Pathela, who led the study, wrote in his report.
"Public health prevention messages should target risky sexual activities, such as unprotected receptive anal sex, and should not be framed to appeal solely to gay-identified men."
The study also found that straight-identified men who have sex with men report fewer sex partners than gay men; straight-identified men who have sex with men report fewer STDs in the past year than gay men; straight-identified men who have sex with men are less likely than gay men to report using a condom during their last sexual encounter; and straight-identified men who have sex with men are more likely to be foreign born than gay men.