Our objective was to determine the level of adherence and reasons for non-adherence to antiretroviral therapy (ART) among HIV-positive (HIV+) people on ART in a resource-limited setting. Patients receiving ART were recruited into the cross-sectional study from three treatment centres in Kampala, Uganda. The number of missed doses over the last three days was assessed by structured patient interviews and dichotomized at +/-95% adherence. Reasons for non-adherence were assessed with both structured patient interviews and unstructured qualitative interviews. Independent predictors of non-adherence were assessed with multivariate logistic regression. In all, 304 HIV-infected persons on ART were enrolled into the study. Factors associated with non-adherence were marital status (odds ratio (OR) = 2.93, 95% confidence interval (CI) 1.32-6.50) and low monthly income <50 US$ [OR = 2.77, 95% CI 1.64-4.67]. We concluded that levels of self-reported adherence in patients receiving ART in Kampala are comparable to levels in resource-rich settings with inability to purchase and secure a stable supply as a major barrier to adherence.