Background The first methadone maintenance treatment (MMT) clinic in Tanzania was launched in February 2011 to address an emerging HIV epidemic among people who inject drugs (PWID). We conducted a retrospective cohort study to understand factors associated with linkage to HIV care and explore how a MMT clinic can serve as a platform for integrated HIV care and treatment. Methods This study utilized routine programmatic and clinical data on clients enrolled in methadone at Muhimbili National Hospital from February 2011 to January 2013. Multivariable proportional hazards regression model were used to examine time to initial CD4 count. Results Final analyses included 148 HIV-positive clients, contributing 31.7 person-years. At 30, 60 and 90 days, the probability of CD4 screening was 40% (95% CI: 32–48%), 55% (95% CI: 47%–63%) and 63% (95% CI: 55%–71%), respectively. Clients receiving high methadone doses (≥85mg/day) [aHR:1.68, 95% CI:(1.03, 2.74)] had higher likelihood of CD4 screening than those receiving low doses (<85 mg/day). Clients with primary education or lower [aHR:1.62, 95% CI:(1.05, 2.51)] and self-reported poor health [aHR:1.96, 95% CI:(1.09, 3.51)] were also more likely to obtain CD4 counts. Clients with criminal arrest history [aHR: 0.56, 95% CI: (0.37, 0.85)] were less likely to be linked to care. Among 17 ART-eligible clients (CD4≤200), 12 (71%) initiated treatment, of which 7 (41%) initiated within 90 days. Conclusions Levels of CD4 screening and ART initiation were similar to Sub-Saharan programs caring primarily for non-PWID. Adequate methadone dosing is important in retaining clients to maximize HIV treatment benefits and allow for successful linkage to services.