Purpose: Despite the benefits of adjuvant endocrine therapy (AET) for reducing recurrence and mortality risks after hormone-sensitive breast cancer, AET adherence is sub-optimal for a high proportion of women. However, little is known about long-term patterns of AET adherence over the minimally recommended 5 years. Our objectives were to: (1) identify 5-year AET adherence trajectory groups; (2) describe trajectory groups according to adherence measures traditionally used (i.e., Proportion of Days Covered); and (3) explore factors associated with trajectories. Methods: We conducted a 5-year cohort study using data from a French national study that included AET dispensing data. Women diagnosed with first non-metastatic breast cancer and having at least 1 AET dispensing in the 12 months after diagnosis were included. Group-based trajectory modeling was used to identify adherence trajectory groups by clustering similar patterns of monthly AET dispensing. Multinomial logistic regressions were used to identify factors associated with trajectories. Results: Among 674 women, five AET adherence trajectory groups were identified: (1) quick decline and stop (5.2% of women); (2) moderate decline and stop (6.4%); (3) slow decline (17.2%); (4) high adherence (30.0%); and (5) maintenance of very high adherence (41.2%). Mean 5-year Proportion of Days Covered varied from 10 to 97% according to trajectories. Women who did not receive chemotherapy or a personalized care plan were more likely to belong to trajectories where AET adherence declined and stopped. Conclusion: Our results provide information on the diversity of longitudinal AET adherence patterns, the timing of decline and discontinuation and associated factors that could inform healthcare professionals.