Background: Body mass index (BMI) has been associated with a risk of esophageal cancer. However, the influence of BMI and BMI loss on people with esophageal cancer that were treated with different therapies has not been described in China. Methods: In total, 615 consecutive patients that underwent esophagectomy and/or chemotherapy/radiotherapy were classified according to the Asian-specific BMI (kg/m(2)) cutoff values. The impact of BMI and BMI loss on long-term overall survival (OS) was estimated using the Kaplan-Meier method and Cox proportional hazard models. Results: Multivariate analysis showed that overweight and obese patients had a more favorable survival than normal weight and underweight patients (p=0.017). Patients with a low BMI and high BMI loss before therapy had worse OS than others (p=0.001). Subgroup analysis showed that patients with a high BMI were more likely to suffer hypertension (p<0.001) and receive only surgery (p<0.001), and they were less likely to be smokers (p=0.007) and anemic (p<0.001). Conversely, patients with high BMI loss were more likely to be anemic (p=0.001), to have advanced pathological stage (p=0.012), and to receive chemotherapy and radiotherapy (p=0.001). Moreover, the mortality rate was higher when patients had a high BMI loss. There is no survival benefit of higher BMI in the non-esophageal squamous cell carcinoma (ESCC) group. Conclusion: Pretreatment BMI was an independent prognostic factor for long-term survival in esophageal cancer patients treated with different treatments. The overall survival was increased in esophageal cancer patients with a high pretreatment BMI and no BMI loss. There is no survival benefit of higher BMI in the non-ESCC group.