PurposeWhile exercise is associated with numerous benefits in women with breast cancer, adherence to exercise training concurrent to cancer treatment is challenging. We aimed to identify predictors of attendance to an oncologist-referred exercise program offered during and after adjuvant breast cancer treatment.MethodsWomen with early-stage breast cancer receiving chemotherapy (n = 68) enrolled in the Nutrition and Exercise During Adjuvant Treatment (NExT) study. Supervised aerobic and resistance exercise was prescribed three times per week during treatment, then one to two times per week for 20 additional weeks. Predictors of attendance were identified using multivariate linear regression for three phases of the intervention, including during (1) adjuvant chemotherapy, (2) radiation, and (3) 20-weeks post-treatment.ResultsHigher baseline quality of life (QoL) predicted higher attendance during chemotherapy (β = 0.51%, 95 CI: 0.09, 0.93) and radiation (β = 0.85%, 95 CI: 0.28, 1.41), and higher QoL, measured at the end of treatment, predicted higher attendance post-treatment (β = 0.81%, 95 CI: 0.34, 1.28). Being employed pre-treatment (β = 34.08%, 95 CI: 5.71, 62.45) and a personal annual income > $80,000 (β = 32.70%, 95 CI: 0.85, 64.55) predicted higher attendance during radiation. Being divorced, separated or widowed (β = − 34.62%, 95 CI: − 56.33, − 12.90), or single (β = − 25.38%, 95 CI: − 40.64, − 10.13), relative to being married/common-law, and undergoing a second surgery (β = − 21.37%, 95 CI: − 33.10, − 9.65) predicted lower attendance post-treatment.ConclusionsDemographic variables, QoL, and receipt of a second surgery significantly predicted attendance throughout the NExT supervised exercise program. These results may help identify individuals with exercise adherence challenges and improve the design of future interventions, including optimizing the timing of program delivery.