The purpose of this meta-analysis was to analyze the available evidence concerning the effects of depression on non-adherence to adjuvant endocrine therapy (AET) in women with breast cancer. MEDLINE and PsycInfo databases from inception through May 1, 2015 were searched using terms related to AET adherence. Articles were reviewed and selected based on predetermined selection criteria, and effect sizes from included studies were extracted. Pooled effect estimates were obtained using random-effects meta-analyses. Of the 312 articles identified, 9 met the inclusion criteria. Overall, depression was significantly associated with non-adherence to AET (Cohen's d = 0.35, 95% CI 0.19-0.52). This effect was not significantly moderated by patient age (<65 vs ≥65 years), length of study follow-up (<18 months vs ≥18 months), or method of assessing adherence (objective vs self-report). However, within these subgroups, significant effects of depression were found only for younger patients (d = 0.46; 95% CI 0.19-0.72) and in studies of shorter duration (<18 months) (d = 0.49; 95% CI 0.22-0.76). These results suggest that AET adherence may be lower among women with greater depressive symptoms, and this effect may be exacerbated in younger women during the early phases (<18 months) of AET. Management of depressive symptoms in women with breast cancer may help in enhancing adherence to AET and improve cancer treatment outcomes.