BackgroundHuman immune deficiency virus (HIV) remains one of the leading causes of infectious disease mortality and morbidity in Sub-Saharan Africa. Although remarkable progress has been made in prevention and treatment of HIV, there is a higher rate of loss to follow-up in HIV-infected children than in adults, once they enter care.ObjectiveTo determine the incidence and identify predictors of loss to follow-up among HIV-infected children on anti-retroviral treatment in Sidama Zone, Ethiopia.MethodsA retrospective cohort study was done among children that were enrolled in ART care in Sidama Zone from September 2014 to August 2018. A total of 143 eligible children were included in this study. A structured checklist was used to extract data from patients’ medical records such as patient intake forms, electronic database, and registers. Data were entered, cleaned, coded, and analyzed by STATA version 12. Cox proportional hazards models were fitted to investigate predictors of loss to follow-up.ResultsOf the 143 participants, 76 (53.15%) were female children with a median age of 7 years and interquartile range of 4–9. The incidence rate was 5 per 100 person-years and the cumulative incidence 12.59%. The median follow-up time was 2.46 years and the total time at risk was 356.06 person-years. Furthermore, 55.56% and 72.22% of those lost to follow-up were within the first and the second years of follow-up, respectively. In multivariable Cox proportional model, only the TB status of the children was significantly associated with loss to follow-up with hazard ratio 3.348 [1.174831, 9.543494] and p-value of 0.024.ConclusionIn this study, TB status of children was the significant determinant of loss to follow-up. However, the overall retention was 87.4% and a substantially higher proportion of loss was observed within the first and second years of follow-up.