Background: Although the prognostic impact of body mass index(BMI) in patients with non?metastatic naso?pharyngeal carcinoma(NPC) had been extensively studied, its effect among metastatic NPC patients remains unknown. The purpose of this study was to evaluate the prognostic effect of BMI in patients with metastatic NPC.Methods: We retrospectively studied 819 patients who were diagnosed with distant metastasis from NPC and received treatment between 1998 and 2007. The patients were divided into three subgroups according to the World Health Organization classifications for Asian populations: underweight(BMI <18.5 kg/m2), normal weight(BMI 18.5–22.9 kg/m2), and overweight/obese(BMI ≥23.0 kg/m2). The associations of BMI with overall survival(OS) and progression?free survival(PFS) were determined by Cox regression analysis.Results: Of the 819 patients, 168(20.5%) were underweight, 431(52.6%) were normal weight, and 220(26.9%) were overweight/obese. Multivariate analysis adjusted for covariates showed that overweight/obese patients had a longer OS than underweight patients [hazard ratio(HR), 0.64; 95% confidence interval(CI), 0.49–0.84] and normal weight patients(HR, 0.72; 95% CI, 0.57–0.90); no significant difference in PFS was observed among these three groups(P = 0.407). Moreover, in stratified analysis, no statistically significant differences in the effect of overweight/obese status among different subgroups were observed.Conclusion: For patients with metastatic NPC, overweight/obese status was associated with longer OS but not longer PFS compared with underweight or normal weight status. Background: Although the prognostic impact of body mass index (BMI) in patients with non? Metastatic naso? Pharyngeal carcinoma (NPC) had been extensively studied, its effect among metastatic NPC patients remains unknown. The purpose of this study was to evaluate the prognostic effect of BMI in patients with metastatic NPC. Methods: We retrospectively studied 819 patients who were diagnosed with distant metastasis from NPC and received treatment between 1998 and 2007. The patients were divided into three subgroups according to the World Health Organization classifications for Asian populations: Underweight (BMI <18.5 kg / m2), normal weight (BMI 18.5-22.9 kg / m2), and overweight / obese (BMI ≥ 23.0 kg / m2) The associations of BMI with overall survival Results: Of the 819 patients, 168 (20.5%) were underweight, 431 (52.6%) were normal weight, and 220 (26.9%) were overweight / obese. Multivariate analysis adjusted for cov ariates showed that overweight / obese patients had a longer OS than underweight patients [hazard ratio (HR), 0.64; 95% confidence interval (CI), 0.49-0.84] and normal weight patients (HR, 0.72; 95% CI, 0.57- No significant difference in PFS was observed among these three groups (P = 0.407); no significant difference in PFS was observed among these three groups NPC, overweight / obese status was associated with longer OS but not longer PFS compared with underweight or normal weight status.