Mortality difference by age, sex, body mass index (BMI) in gastric cancer (GC) has been controversial. We evaluated sex-specific mortality by age and BMI. A total of 5961 patients diagnosed with GC from 2005 to 2013 in a single tertiary center were included and were followed until December 2017. The plot in goodness-of-fit-test by sex was crossed, so we performed sex-specific analysis. Overall mortality was lower in women than in men (adjusted hazard ratio [aHR], 0.72). Favor outcomes in women compared to men were observed among patients older than 60 yr (aHR, 0.64; 95% CI, 0.56-0.74), a BMI less than 25 kg/m(2) (aHR, 0.69; 95% CI, 0.61-0.79), and stage I (aHR, 0.46; 95% CI, 0.38-0.56). In sex-specific analysis, mortality increased in age older than 60 yr in men, whereas it increased in both extreme ages ( < 40 yr and >= 70 yr) in women. Mortality by BMI was lowest at BMI of 25-29.9 kg/m(2) and gradually increased according to decrease of BMI in men; aHR, 1.24 (23-24.9 kg/m(2)), 1.44 (18.5-22.9 kg/m(2)), and 2.54 (BMI < 18.5 kg/m(2)). However, mortality decreased in patients with BMI >= 30 kg/m(2) (aHR, 0.46) in women. The sex discrepancies in GC mortality by age and BMI suggest the need for sex-specific approaches to prognostic prediction. (C) 2021 Editrice Gastroenterologica Italiana S.r.l. Published by Elsevier Ltd. All rights reserved.