This study purposed to explore the impact of hospital volume and surgeon volume on hospital resource utilization after bariatric surgery and to identify the predictors of length of stay (LOS) and hospital treatment cost in a nationwide population in Taiwan.This population-based cohort study retrospectively analyzed 2,674 bariatric surgery procedures performed from 1997 to 2008. Hospitals were classified as low- and high-volume hospitals if their annual number of bariatric surgeries were < 35 and a parts per thousand yen35, respectively. Surgeons were classified as low- and high-volume surgeons if their annual number of bariatric surgeries were < 15 and a parts per thousand yen15, respectively. Hierarchical linear regression models were used to predict LOS and hospital treatment cost.The mean LOS was 7.67 days and the LOS for high-volume hospitals/surgeons was, on average, 28%/31% shorter than that for low-volume hospitals/surgeons. The mean hospital treatment cost was US$2,344.08, and the average hospital costs for high-volume hospitals/surgeons were 10%/13% lower than those for low-volume hospitals/surgeons. Advanced age, male gender, high Charlson co-morbidity index, and current treatment in a low-volume hospital, by a low-volume surgeon, and via open gastric bypass were significantly associated with long LOS and high hospital treatment cost (P < 0.001).The data suggest that annual surgical volume is the key factor in hospital resource utilization. The results improve the understanding of medical resource allocation for this surgical procedure and can help to formulate public health policies for optimizing hospital resource utilization for related diseases.