|| We investigated the relationship between body mass index (BMI) and postoperative outcomes in 450 gallbladder cancer patients in Japan. We collected patient information, including sex, age, underlying disease, BMI, stage, surgery method, postoperative time to discharge, and postoperative Medicare fees, from the Japanese administrative database associated with the Diagnosis Procedure Combination system. We classified patient BMIs as underweight (BMI<18.5 kg/m2), normal (BMI≥18.5 kg/m2 and <25 kg/m2) or overweight/obese (BMI≥25 kg/m2), then investigated the relationship between these categories and two postoperative outcomes: time to discharge and postoperative Medicare fees. The median postoperative time to discharge was 12 days in all patients, and 12 days in each of the three weight groups (p=0.62, n.s.). The median postoperative Medicare fees from surgery until discharge were (USD): all patients, $5,002; underweight, $5,875; normal weight, $4,797; and overweight/obese, $5,179 (p=0.146, n.s.). A multivariate analysis with adjustment for competing risk factors revealed that BMI was not associated with increased risk of longer postoperative time to discharge (normal weight: HR 1.17, p=0.29; overweight/obese: HR 1.17, p=0.37) or higher postoperative Medicare fees (OR 0.99, p=0.86, n.s.). Thus, high BMI was not found to be a factor for poor postoperative outcomes in Japanese patients with gallbladder cancer.