BackgroundPerihilar cholangiocarcinoma (pCCA) is a malignant tumor of the hepatobiliary system which is still associated with a challenging prognosis. Postoperative complications play a crucial role in determining the overall prognosis of patients with pCCA. Changes in body composition (BC) have been shown to impact the prognosis of various types of tumors. Therefore, our study aimed to investigate the correlation between BC, postoperative complications and oncological outcome in patients with pCCA.MethodsAll patients with pCCA who underwent curative‐intent surgery for pCCA between 2010 and 2022 were included in this analysis. BC was assessed using preoperative computed tomography and analyzed with the assistance of a 3D Slicer software. Univariate and multivariate binary logistic regression analyses were conducted to examine the relationship between BC and clinical characteristics including various measurements of postoperative complications and Cox regressions and Kaplan–Meier analysis to evaluate oncological risk factors in the study cohort.ResultsBC was frequently altered in patients undergoing curative‐intent liver resection for pCCA (n = 204) with 52.5% of the patients showing obesity, 55.9% sarcopenia, 21.6% sarcopenic obesity, 48.5% myosteatosis, and 69.1% visceral obesity. In multivariate analysis, severe postoperative complications (Clavien‐Dindo ≥3b) were associated with body mass index (BMI) (Odds ratio (OR) = 2.001, p = 0.024), sarcopenia (OR = 2.145, p = 0.034), and myosteatosis (OR = 2.097, p = 0.017) as independent predictors. Furthermore, sarcopenia was associated with reduced overall survival (OS) in pCCA patients (sarcopenia vs. no‐sarcopenia, 21 months vs. 32 months, p = 0.048 log rank).ConclusionsBC is highly associated with severe postoperative complications in patients with pCCA and shows tendency to be associated impaired overall survival. Preoperative assessment of BC and interventions to improve BC might therefore be key to improve outcome in pCCA patients undergoing surgical therapy.