BACKGROUND: Anogenital human papillomavirus (HPV) is common among men who have sex with men (MSM) and causes anal cancer. This study examined the determinants of initial anogenital HPV infection among teenage MSM. METHODS: Two hundred MSM aged 16 to 20 years were recruited via community and other sources. Men were tested for HPV DNA from the anus and penis. RESULTS: The proportion of men with anal HPV of any type increased from 10.0% in men reporting no prior receptive anal sex to 47.3% in men reporting ≥ 4 receptive anal sex partners (P < .001).A similar pattern was also seen with HPV type 16 (P = .044). The proportion of men with penile HPV increased from 3.7% in men reporting no prior insertive anal sex to 14.8% in men reporting ≥ 4 insertive anal sex partners (P = .014). Overall, 39.0% (95% confidence interval (CI), 32.2%-46.1%) of men had at least 1 HPV type: 23.0% (95% CI, 17.4%-29.5%) had a vaccine-preventable type (6, 11, 16 or 18). CONCLUSIONS: Early and high per partner transmission of HPV occurred between men soon after their first sexual experiences. HPV vaccination needs to commence early for maximal prevention of HPV among MSM.