The aim of this study was to quantify the hormone therapy (HT) nonadherence patterns and to assess the associated risk factors in Asian women with breast cancer. This retrospective cohort study used the Taiwan Health Insurance Research Database from 2003 to 2011. Data from women with newly diagnosed primary breast cancer were identified, and persistence (without HT prescribing gap ≥ 180 days) to HT was defined through records of dispensing prescriptions. Study cohorts were further classified as adjuvant and primary HT groups. Each individual's HT utilization patterns and the medication possession ratio at overall HT course were measured. The odds ratios (ORs) of nonadherence (medication possession ratio, <80%) in adjuvant and primary HT patients were estimated using logistic regressions with adjustment of potential confounding variables. These patients had 15.6% and 23.4% nonadherence rates to HT in adjuvant and primary HT groups, respectively. In the adjuvant HT group, older age groups (≥50 years) and taking aromatase inhibitors were less likely to show nonadherence (p < 0.05). In the primary HT group, women older than 70 years were significantly less likely to exhibit nonadherence (OR = 0.53; 95% confidence interval, 0.28-0.99); however, women with presence of HT-related adverse events had significantly increased risk (OR = 1.44; 95% confidence interval, 1.02-2.03). Young age and experience of musculoskeletal and joint symptoms were identified as risk factors for nonadherence.