Background: A fraction of HIV-diagnosed individuals promptly initiate antiretroviral therapy (ART). We evaluated the efficacy of health system navigators for improving linkage to HIV and tuberculosis (TB) care among newly diagnosed HIV-infected outpatients in Durban, South Africa. Methods: We conducted a randomized controlled trial (Sizanani Trial, NCT01188941) among adults (≥18 years) at 4 sites. Participants underwent TB screening and randomization into a health system navigator intervention or usual care. Intervention participants had an in-person interview at enrollment and received phone calls and text messages over 4 months. We assessed 9-month outcomes via medical records and the National Population Registry. Primary outcome was completion of at least 3 months of ART or 6 months of TB treatment for coinfected participants. Results: Four thousand nine hundred three participants were enrolled and randomized; 1899 (39%) were HIV-infected, with 1146 (60%) ART-eligible and 523 (28%) TB coinfected at baseline. In the intervention, 212 (39% of outcome-eligible) reached primary outcome compared to 197 (42%) in usual care (RR 0.93, 95% CI: 0.80 to 1.08). One hundred thirty-one (14%) HIV-infected intervention participants died compared to 119 (13%) in usual care; death rates did not differ between arms (RR 1.06, 95% CI: 0.84 to 1.34). In the as-treated analysis, participants reached for ≥5 navigator calls were more likely to achieve study outcome. Conclusions: ∼40% of ART-eligible participants in both study arms reached the primary outcome 9 months after HIV diagnosis. Low rates of engagement in care, high death rates, and lack of navigator efficacy highlight the urgency of identifying more effective strategies for improving HIV and TB care outcomes