Purpose: This study examined the nutritional status of patients with hepatobiliary-pancreatic diseases before surgery to establish basic reference data. Materials and Methods: This study evaluated retrospectively 2,322 patients admitted for hepatobiliary-pancreatic surgery between 2014 and 2016 at four Korean medical institutions using the body mass index (BMI) score. The prognostic nutrition index (PNI) was calculated in patients diagnosed with malignant diseases. Results: The mean BMI was 24.0 kg/m2 (range, 13.2~39.1 kg/m2). The patients were classified as low BMI (<21.5 kg/ m2, below 25 percentile), intermediate BMI (21.5~25.5 kg/m2), and high BMI (>25.5 kg/m2, above 75 percentile). There were significant differences in the age, sex distribution, ASA classification, type of hospitalization, biliary drainage, organ, and pathology diagnosis between the pairs among the low, intermediate, and high BMI groups. Among the three BMI groups, the complication rate of the low BMI group was highest (34.4% vs. 29.7% vs. 25.8% P=0.005). The median lengths of hospital stay in the low, intermediate, and high BMI groups were 9, 9, and 7 days, respectively (P<0.001). Multivariate analysis revealed the risk factors of the low BMI group to be a higher ASA classification, biliary drainage, pancreatic disease, and malignant disease. The group with PNI<45 had significantly longer hospital stays than the group with PNI≥45 (P<0.001). Conclusion: Patients with a low BMI had a higher ASA classification, preoperative biliary drainage, pancreatic disease, and malignant disease. The low PNI group had significantly longer hospital stays than the high PNI group. Screening of the preoperative nutritional status is necessary for assessing the risk of malnutrition and its treatment.