BACKGROUND: This study generated new information about the outcomes of patients enrolled in antiretroviral treatment programmes, as well as the true outcomes of those lost to follow-up (LTF). METHODS: Anonymized data were collected for patients enrolled over a 12-month period from two programmes (public and private) in southeast Nigeria. Estimates of retention, LTF, mortality and transfers were computed. All LTF enrollees (defined as patients who had missed three scheduled visits) whose contact information met pre-defined criteria were traced. RESULTS: A total of 481 (public) and 553 (private) records were included. Median duration of follow-up was about 14 months. Cumulative retention and LTF proportions were 66·5 and 32·8% (public), and 82·6 and 11·0% (private) respectively. LTF rates at third, sixth, ninth and twelfth months were 7·5, 19·3, 25·4 and 29·6% respectively (public), and 4·1, 7·1, 9·0 and 10·0% (private). LTF was higher among males, patients with CD4(+) cell count ≤200 and public programme enrollees. For the public facility, 56·7% of 104 traceable patients were dead and 38·8% were alive; the figures were 34·2 and 60·5% of 46 patients respectively for the private. Most deaths had occurred by the third month. CONCLUSION: Not all patients enrolled for treatment were retained. Though some died, many were LTF, lived within the community, and could develop and transmit resistant viral stains. Most traced patients were dead by the third month and poor contact information limited the effectiveness of tracing. Antiretroviral treatment programmes need to improve documentation processes and develop and implement tracing strategies.