We compared self-described HIV-positive (31.6%, n=445), HIV-negative (56.8%, n=801), and HIV-unknown (11.6%, n=164) gay and bisexual men (GBM) on sociodemographic and behavioral characteristics. Participants from across the U.S. were enrolled via a popular sexual networking website to complete an online survey. In total, 44.8% of HIV-negative and HIV-unknown men said they had not been tested for HIV in the CDC-recommended last 6 months. HIV-unknown men significantly differed from HIV-negative and HIV-positive men in sexual behavior and HIV status disclosure patterns. HIV-unknown men were more willing than HIV-negative men to take PrEP; however, HIV-unknown men were significantly less likely than others to have health insurance or a primary care provider. Given the observed differences, researchers should consider analyzing men who are HIV-unknown distinctly from HIV-negative and HIV-positive men.