Body mass index (BMI) is a risk factor for comorbid illnesses and cancer development. It was hypothesized that obesity status affects disease outcomes and treatment-related toxicities in esophageal cancer patients treated with chemoradiotherapy (CRT). From March 2002 to April 2010, 405 patients with non-metastatic esophageal carcinoma at MD Anderson Cancer Center treated with either definitive or neoadjuvant CRT were retrospectively analyzed. Patients were categorized as either obese (BMI ≥ 25 kg/m2) or nonobese (BMI < 25 kg/m2). Progression-free survival and overall survival times were examined using the Kaplan–Meier method and Cox proportional hazards regression analysis. One hundred fifteen (28.4%) patients were classified as nonobese and 290 (71.6%) as obese. Obese patients were more likely than others to have several comorbid diseases (P < 0.001), adenocarcinoma located distally (P < 0.001), and have undergone surgery (P = 0.004). Obesity was not associated with either worse operative morbidity/mortality (P > 0.05) or worse positron emission tomography tumor response (P = 0.46) on univariate analysis, nor with worse pathologic complete response (P = 0.98) on multivariate analysis. There was also no difference in overall survival, locoregional control, or metastasis-free survival between obese and nonobese patients (P = 0.86). However, higher BMI was associated with reduced risk of chemoradiation-induced high-grade esophagitis (P = 0.021), esophageal stricture (P < 0.001), and high-grade hematologic toxicity (P < 0.001). In esophageal cancer patients treated with CRT, obesity is not predictive of poorer disease outcomes or operative morbidities; instead, data suggest it may be associated with decreased risk of acute chemotherapy- and radiotherapy-related treatment toxicities.