Background: Reporting mortality and lost to follow-up (LTFU) by age is essential as older HIV-positive patients might be at risk of long-term effects of living with HIV and/or taking antiretroviral therapy (ART). As age effects might not be linear and might impact HIV outcomes in the oldest more severely, people living with HIV (PLHIV) aged 50-59 years and PLHIV aged >60 years were considered separately. Setting: Seventeen adult HIV/AIDS clinics spread over nine countries in West Africa. Methods: Data were collected within the International Epidemiological Databases to Evaluate AIDS West Africa Collaboration. ART-naive PLHIV-1 adults aged >16 years initiating ART and attending >= 2 clinic visits were included (N=73,525). Age was divided into five groups: 16-29/30-39/40-49/50-59/>= 60 years. The age effect on mortality and LTFU was evaluated with Kaplan-Meier curves and multivariable Cox proportional hazard regressions. Results: At month 36, 5.9% of the patients had died and 47.3% were LTFU. Patients aged >= 60 (N=1,736) and between 50-59 years old (N=6,792) had an increased risk of death in the first 36 months on ART (adjusted hazard ratio=1.66; 95% CI: 1.36-2.03 and adjusted hazard ratio=1.31; 95% CI: 1.15-1.49, respectively; reference: <30 years old). Patients >= 60 years old tend to be more often LTFU. Condusion: The oldest PLHIV presented the poorest outcomes, suggesting that the PLHIV aged >50 years old should not be considered as a unique group irrespective of their age. Tailored programs focusing on improving the care services for older PLHIV in Sub-Saharan Africa are clearly needed to improve basic program outcomes.< Réduire