Objective: Fixed incentives have been largely unsuccessful in improving adherence to antiretroviral medication. Therefore, we evaluate whether small incentives based on behavioral economic theory can increase adherence to antiretroviral medication among treatment-mature adults in Kampala, Uganda. Design: A randomized control trial design tests whether providing small incentives based on either attending timely clinic visits (intervention group 1) or achieving high medication adherence (intervention group 2) can increase antiretroviral adherence. Antiretroviral adherence is measured by medical event monitoring system (MEMS) caps. Methods: Overall, 155 HIV-infected men and women age 19-78 were randomized into one of two intervention groups and received small prizes of US $ 1.50 awarded through a drawing conditional on either attending scheduled clinic appointments or achieving at least 90% antiretroviral adherence. The control group received the usual standard of care. Results: Preliminary results based on pooling the intervention groups showed individuals receiving incentives were 23.7 percentage points more likely to achieve 90% antiretroviral adherence compared with the control group [95% confidence interval (CI), 6.7-40.7%]. Specifically, 63.3% (95% CI, 52.9-72.8%) of participants in the pooled intervention groups maintained at least 90% mean adherence during the first 9 months of the intervention, compared with 39.6% (95% CI, 25.8-54.7%) in the control group. Conclusion: Small prize incentives resulted in a statistically significant increase in antiretroviral adherence. Although more traditional fixed incentives have not produced the desired results, these findings suggest that small incentives based on behavioral economic theory may be more effective in motivating long-term adherence among treatment-mature adults. Copyright (C)2017 Wolters Kluwer Health, Inc. All rights reserved.