Obesity, which is becoming endemic in the United States, causes a significant challenge for reconstructive surgeons. This study evaluates postoperative complications and impact of weight loss in the high body mass index (BMI) population undergoing breast reconstruction with abdominal free flaps. A retrospective review of 182 consecutive patients was performed. Patients were divided into groups according to their BMI at the time of surgery (preoperative BMI) and presence of weight loss, and data were compared among groups. Multivariate analysis of effect of preoperative BMI on complications revealed that overall flap (P = 0.008) and donor (P = 0.016) complication rates were significantly higher in the obese group. Analysis of preoperative weight loss did not yield a statistically significant reduction in flap (P = 0.5161) or donor (P = 0.8034) complication rates. Univariate analysis showed that higher preoperative BMI is associated with higher risk of systemic complications (P = 0.027). It is important to inform patients preoperatively that weight loss, although beneficial for ease of procedure and quality of life, does not diminish their increased risk of complications. Body mass index during surgery is the most important predictor of complications.