Obesity and overweight are established risk factors for the development of breast cancer. They are also associated with poor prognosis for higher risk of disease recurrence and lower overall survival (OS). The aim of this study was to evaluate the influence of overweight and obesity in OS in patients with locally advanced breast cancer (LABC) treated with neoadjuvant chemotherapy. This is a retrospective analysis that included 819 patients diagnosed with LABC between January 2004 and December 2008. The patients were treated with neoadjuvant chemotherapy (NAT) based on anthracyclines, taxanes, or both, followed by surgery. For comparison, patients were divided into the normal weight (NW) group or the overweight/obesity (OW/OB) group. The prevalence of overweight/obesity was 74 %. General characteristics of the patients, including age, tumor size, clinical stage, nuclear grade, hormone receptors, and HER2 expression, were similar between both groups. At a median follow-up of 28 months, we found a statistically significant difference in OS between the two groups, achieving a 91.5 % in NW patients versus 85.9 % in the OW/OB group (P = 0.050). Cox multivariate analysis demonstrated that obesity was an independent factor for poor prognosis, with a hazard ratio of 1.79 (95 % CI (Confidence Interval) 1.09–2.96; P = 0.022). This is the first Mexican study that confirms the role of OW/OB as a risk factor for poor outcome among patients with LABC. Obesity in our country is a public health problem and requires strong preventive intervention strategies for its control, especially among patients diagnosed with breast cancer.