BACKGROUND: Adherence to combination anti-retroviral therapy for HIV infection is a primary determinant of treatment success, but is often suboptimal. Previous studies have suggested that electronic medication monitoring-informed counseling is among the most effective adherence intervention components. Our objective was to review available evidence about the effectiveness of monitoring-informed counseling and to aggregate findings into quantitative estimates of the effect of such intervention on medication adherence and virologic treatment outcomes. METHODS: We searched PubMed for papers reporting on randomized controlled trials comparing intervention groups receiving monitoring-informed counseling as one of the intervention components versus control groups not receiving such counseling for their effect on medication adherence and viral load concentrations. The standardized mean difference (SMD) in adherence and the odds ratio (OR) of undetectable HIV RNA in intervention versus control groups were the common effect sizes. Random-effect models with inverse variance weights were used to aggregate findings into pooled effect estimates with 95% confidence limits (CI). RESULTS: A total of 13 studies were included. Adherence was significantly higher in intervention groups than in control groups (SMD 0.51, 95% CI 0.31-0.71). Patients in intervention groups were significantly more likely to have undetectable HIV RNA concentrations than patients in control groups (OR 1.35, 95% CI 1.12-1.63). However, in studies in which monitoring-informed counseling was the only intervention component, the difference in adherence and virologic response between intervention and control groups was not statistically significant. CONCLUSION: Electronic monitoring-informed counseling improved adherence and virologic response compared with control groups not receiving such counseling in studies in which it was one out of multiple intervention components, but not in studies where it was the only intervention component.