OBJECTIVE To describe reasons for exclusion from isoniazid tuberculosis preventive therapy (IPT) and outcomes of persons living with HIV (PLWH) during 6 months of IPT. METHODS In a clinical trial conducted in government clinics, first screening (screen 1) used National IPT Program guidelines and a second screening (screen 2) was trial specific. Adherence was defined as attending 6 monthly visits. RESULTS Between 2004 and 2006, at 4018 screening visits, 2934 (73%) PLWH met screen 1 criteria; 1995 (68%) met screen 2 criteria and were enrolled. Major reasons for exclusion were illness (66%) at screen 1 and abnormal chest radiographs (36%) at screen 2. Tuberculin skin tests were > or = 5 mm in 24% of those enrolled and 31% had CD4 lymphocyte counts <200 cells/mm(3). During the 6 months, 8 (0.40%) developed tuberculosis disease, 28 (1.4%) had severe adverse events (19/28 were hepatitis including one death probably isoniazid-associated), 20 others died, and 22% initiated antiretroviral therapy (ART). Although adherence was 86%, being on ART improved adherence: relative risk 1.41 (95% confidence limits 1.04-1.91). In multivariate analysis, ART was associated with a 4.38 greater odds of adherence to IPT. CONCLUSIONS Six months of IPT was relatively safe and well-tolerated by PLWH. Adherence to IPT was significantly better among those receiving ART with IPT.