Men who have sex with men (MSM) are typically studied as though they were a homogeneous population. This has resulted in a lack of knowledge about the sexual health and behavior of bisexual men as distinct from gay men. In this study, patterns of sexual behavior and rates of HIV testing were compared between 854 gay-identifying and 164 bisexual-identifying men who participated in an Australian nationwide online survey. Approximately half of both groups engaged in unprotected anal intercourse (UAI) at their most recent sexual encounter, but bisexual-identifying men were more likely to have had sex with a partner who was either serodiscordant or with whom their seroconcordance was unknown. Despite these patterns, only 62% of bisexual-identifying men had ever been tested for HIV compared to 84% of gay-identifying men. Multivariate logistic regression focused on rates of UAI and HIV testing among bisexual-identifying men. Patterns were similar across all age groups and educational backgrounds. However, bisexual-identifying men were less likely to engage in UAI with a casual partner and were more likely to have been tested for HIV if they had multiple partners or had disclosed their sexual orientation to their social networks. In all, these data reveal important differences between gay- and bisexual-identifying men, particularly with regard to HIV testing, and highlight a need for HIV prevention strategies to focus more strategically on finding ways of promoting safer sex and HIV testing among all MSM.