Abstract: Many, but not all patients experience weight gain 1 year after a breast cancer diagnosis; clearly defined, clinically relevant groups at risk of weight gain have yet to be described. We set out to determine the factors associated with weight gain over time in patients with invasive breast cancer during a period of predominantly anthracycline-based adjuvant chemotherapy and to identify groups with differing weight gain risks. Breast cancer patients (stage I–IIIB) were identified in a retrospective chart review. Evaluated parameters included weight at diagnosis and 1, 2, and 3 years later, height, body mass index (BMI), age, menopausal and change in menopausal status, as well as therapy and pathologic stage. Regression models identified significant independent predictors of weight change. Recursive partitioning analysis (RPA) was employed to divide the dataset into relevant and significant groups. In 185 identified patients, regression models and RPA demonstrated that weight gain at 1 year was associated with younger age, adjuvant chemotherapy, and lower BMI. Weight gain at 2 years (n = 176) was greater than at year 1, and in addition to weight gain at year 1, was associated with younger age and adjuvant chemotherapy in regression analysis; RPA found that anthracycline therapy, age, and BMI were important. Weights at 3 years were similar to those seen at 2 years. Early-stage breast cancer patients treated with chemotherapy continue to gain weight 2 years after diagnosis, and this weight gain appears to be persistent at year 3. Observation beyond 1 year is needed to adequately evaluate weight gain in early-stage breast cancer patients, particularly for those receiving contemporary adjuvant chemotherapy.