OBJECTIVE: Chemotherapy-induced cognitive impairments are reported by many cancer survivors. Research to date has not provided a clear description of their nature, extent, mechanisms, and duration. To investigate the impairments and factors that could influence their identification and severity, the present meta-analysis brings together research on this topic in adult cancer patients. METHOD: Our random-model meta-analysis includes 44 studies investigating the cognitive performance of adults treated with chemotherapy for non-central nervous system malignancies, primarily breast and testicular cancer. We conducted several subgroup analyses to identify the level of cognitive impairments in longitudinal and cross-sectional studies. We also pursued several multilevel model regressions to investigate the impact of methodological (study quality) and clinical moderators (diagnosis, age, time since treatment) on the observed effect sizes. RESULTS: Cognitive impairments were found in cross-sectional studies in immediate free recall, delayed memory, verbal memory, delayed recognition memory, selective attention, and attention capacity. Surprisingly, prior to chemotherapy, patients performed better than matched controls. In longitudinal studies, patients' performance increased from baseline to follow-up, an effect that was stronger in patients than controls. None of the chosen moderators influenced the magnitude of estimated summary effect sizes. CONCLUSIONS: The likelihood to identify impairments rests on the type of design employed, as memory and attention impairments are only detected in cross-sectional studies. We discuss the lack of significant impact of moderators on the effect sizes despite the heterogeneity of results, while providing recommendations toward decreasing the heterogeneity in future studies. (PsycINFO Database Record (c) 2014 APA, all rights reserved).