BACKGROUND: Expanded access to antiretroviral therapy (ART) leads to improved HIV/AIDS treatment outcomes in Nigeria, however, increasing rates of loss to follow-up among those on ART is threatening optimal standard achievement. Therefore, this retrospective cross-sectional study is aimed at identifying correlates and predictors of loss to follow-up in patients commencing ART in a large HIV program in Nigeria. METHODS: Records of all patients from 432 US CDC Presidents Emergency Plan for AIDS Relief (PEPFAR) supported facilities across 10 States and FCT who started ART from 2004 to 2017 were used for this study. Bivariate and multivariate analysis of the demographic and clinical parameters of all patients was conducted using STATA version 14 to determine correlates and predictors of loss to follow-up. RESULTS: Within the review period, 245,257 patients were ever enrolled on anti-retroviral therapy. 150,191 (61.2%) remained on treatment, 10,960 (4.5%) were transferred out to other facilities, 6926 (2.8%) died, 2139 (0.9%) self-terminated treatment and 75,041 (30.6%) had a loss to follow-up event captured. Males (OR: 1.16), Non-pregnant female (OR: 4.55), Patients on ≥ 3-monthly ARV refills (OR: 1.32), Patients with un-suppressed viral loads on ART (OR: 4.52), patients on adult 2nd line regimen (OR: 1.23) or pediatric on 1st line regimen (OR: 1.70) were significantly more likely to be lost to follow-up. CONCLUSION: Despite increasing access to anti-retroviral therapy, loss to follow-up is still a challenge in the HIV program in Nigeria. Differentiated care approaches that will focus on males, non-pregnant females and paediatrics is encouraged. Reducing months of Anti-retroviral drug refill to less than 3 months is advocated for increased patient adherence.