Despite progress on population-level HIV viral suppression, unknown outcomes amongst people who have initiated antiretroviral therapy (ART) in low- and middle-income countries, commonly referred to as loss to follow-up (LTFU), remains a barrier. The mean global estimate of LTFU is 20%, exceeding the World Health Organization target of <15%. Pervasive predictors associated with LTFU include younger age, low body mass index, low CD4 count, advanced HIV clinical stage and certain ART regimens. In Namibia, ART use by eligible individuals exceeds 85%, surpassing the global average. Nonetheless, LTFU remains a barrier to achieving viral suppression and requires research to elucidate context-specific factors. An observational cohort study was conducted in Namibia in 2012 by administering surveys to individuals who presented for HIV care and initiated ART for the first time. Additional data were collected from routine medical data monitoring systems. Participants classified as LTFU at 12 months were traced to confirm their status. Predictors of LTFU were analyzed using multivariable logistic regression. Of those who presented consecutively to initiate ART, 524 were identified as eligible to enroll in the study, 497 enrolled, and 474 completed the baseline questionnaire. The cohort had mean age 36 years, 39% were male, mean CD4 cell count 222 cells/mm3, 17% were WHO HIV clinical stage III-IV, and 14% started efavirenz-based regimens. Tracing participants classified as LTFU yielded a re-categorization from 27.8% (n = 132) to 14.3% (n = 68) LTFU. In the final multivariable model, factors associated with confirmed LTFU status were: younger age (OR 0.97, 95% CI 1.00-1.06, p = 0.02); male sex (OR 2.34, CI 1.34-4.06, p = 0.003); difficulty leaving work or home to attend clinic (OR 2.55, CI 1.40-4.65, p = 0.002); and baseline efavirenz-based regimen (OR 2.35, CI 1.22-4.51, p = 0.01). Interventions to reduce LTFU should therefore target young men, particularly those who report difficulty leaving work or home to attend clinic and are on an efavirenz-based regimen.