Background: Obesity is associated with reduced risk of developing lung cancer (LC), but its effect on LC mortality remains unclear. We performed a systematic review and meta-analysis to assess the association between premorbid body mass index (BMI) and LC mortality. Methods: Conducting a systematic search of MEDLINE and the Cochrane library through December 2015, we identified observational studies reporting the association between premorbid BMI, and mortality in LC patients. We estimated summary adjusted hazard ratio (aHR) with 95% confidence intervals (CI), comparing highest vs. lowest BMI category, and obese (BMI > 30 kg/m2) and overweight (BMI 25-29.9 kg/m2) categories with reference category in each study, using random effects model; heterogeneity was measured using the inconsistency index (I2). Results: 16 studies were initially identified of which 5 were excluded since data did not allow for estimation of aHR using predefined obesity categories. 11 studies (including 1 pooled cohort study) comprising 2,953,278 individuals at inception, in whom 27,282 LC deaths occurred were analysed. On meta-analysis, highest vs lowest BMI category was associated with 33% reduction in LC mortality (11 studies, aHR, 0.67; 95% CI, 0.54-0.82; I²= 90%). After exclusion of one study which was contributing to considerable heterogeneity, a significant 21% reduction in LC mortality was a more conservative, consistent estimate (aHR, 0.79; 95% CI, 0.73-0.85; I²= 26%). Compared with LC patients with normal BMI, a reduction in mortality in both overweight [9 studies, aHR, 0.83; 95% CI, 0.78-0.89; I²= 68%] and obese [9 studies, aHR 0.80, 95% CI; 0.74-0.87; I²= 45%] individuals was seen, p-value between obese and overweight vs normal, 0.30). On subgroup analysis by sex and smoking status, no difference was noted between men vs women, and never smokers vs ever-smokers. Conclusions: Based on meta-analysis, obese and overweight LC patients have reduced mortality compared to leaner individuals. There was no clear dose response relationship between BMI and LC mortality in our study. The protective effect was seen across sexes and smoking status. Ideal body weight in LC patients should be reconsidered.