Aims: The prognostic role of BMI variation during and/or after treatments for early-stage breast cancer is still unknown. Patients & methods: The χ2 test was conducted to explore the correlation between breast cancer recurrence and BMI changes in 520 early-stage breast cancer patients. Cox proportional hazard models were used to analyze the association of BMI changes, baseline BMI, known prognostic factors and recurrences. Results: BMI gain was significant determinant of recurrences (p = 0.0008). In multivariate analyses, BMI variation more than 5.71% was associated with higher rates of recurrences, as well as age less than 55 years, stage disease and molecular subtype. Conclusion: Women who experience BMI gain after breast cancer may be at increased risk of poor outcomes.