BACKGROUND Adjuvant hormonal therapy is crucial in the treatment of estrogen receptor-positive breast cancer. The nonadherence rate to hormonal treatment is reported to be as high as 60%. The goal of this study was to evaluate the factors evoked by the patients as well as the demographic and disease-related factors that could be associated with nonadherence to adjuvant hormonal therapy. METHODS All consecutive patients treated for an estrogen receptor-positive breast cancer who showed up for regular follow-up with a single breast specialist between November 2008 and April 2009 were included in the study. We assessed adherence to hormonal therapy (either with tamoxifen or aromatase inhibitor). Reasons for adherence and nonadherence were collected. Records were also reviewed for demographic and cancer characteristics and for treatment components. RESULTS We included 161 patients in the study; 150 (93.2%) adhered to hormonal treatment. Side effects and absence of conviction were the main reasons for nonadherence. The importance of the diagnosis of cancer, fear of recurrence and regular follow-up were reported as the main reasons for adherence. CONCLUSIONS Severity of disease and side effects are associated with nonadherence to treatment. Strict follow-up appears to be a necessary adjunct in the adherence to treatment. The association between demographic and cancer characteristics and treatment components needs further investigation. However, these factors may help identify patients at risk of nonadherence and help the oncology team.