Among young men who have sex with men (MSM) surveyed in six US cities, we evaluated the magnitude and correlates of perceived lifetime risk for acquiring HIV, and missed opportunities to increase risk perception by providers of health-care and HIV-testing services. Overall, approximately one quarter of young MSM perceived themselves at moderate/high risk for acquiring HIV. Adjusting for demographic, prior testing, and behavioral characteristics, moderate/high perceived risk had the strongest association with unrecognized HIV infection. However, half of the 267 young MSM with unrecognized infection perceived themselves at low lifetime risk for acquiring HIV, and many young MSM with low-risk perception reported considerable risk behaviors. Providers of health-care and HIV-testing services missed opportunities to assess risks and recommend testing for young MSM. To increase HIV testing, prevention providers should intensify efforts to assess, and to increase when needed, perceptions of lifetime risks for acquiring HIV among young MSM.