BACKGROUND: Sexual and gender minorities (SGM) bear a high burden of HIV. The age of anal sexual debut may influence HIV care engagement. Our objective was to evaluate this relationship to help health care providers promote and anticipate future HIV care engagement among at-risk SGM. METHODS: The TRUST/RV368 study provided HIV testing and treatment at SGM-friendly clinics in Abuja and Lagos, Nigeria. Self-reported age of sexual debut was dichotomized as <16 or ≥16 years. Multivariable logistic models estimated adjusted odds ratios (aOR) and 95% confidence intervals (CI) for the association of sexual debut with (1) HIV testing history, (2) HIV testing at the clinics, (3) initiation of antiretroviral therapy (ART) within 6 months of a clinic diagnosis, and (4) viral suppression within 12 months of ART initiation. RESULTS: Of the 2680 participants, 30% (n = 805) reported a sexual debut <16 years. Those with an <16-year debut had significantly more receptive sex partners, condomless sex, and transactional sex (all P < 0.01) and were 24% less likely to have tested for HIV before enrollment (aOR: 0.76; CI: 0.62 to 0.93). However, <16-year debut was not associated with HIV testing, receiving ART, or achieving viral suppression once engaged with TRUST/RV368 (all P > 0.05). CONCLUSIONS: SGM with <16-year debut engaged in behaviors that could increase HIV risk and were less likely to have a history of HIV testing. However, once enrolled in SGM-friendly clinics, uptake of HIV care was not associated with <16-year debut, suggesting that SGM-friendly care models may promote HIV care engagement.