Background/Aims: Postoperative delirium (POD) is one of the most common complications after various types of surgery. The aim of this study was to investigate the incidence and risk factors for delirium after pancreaticoduodenectomy (PD). Methods: This was a retrospective study of 146 consecutive patients who underwent PD between April 2007 and June 2015 at Saiseikai Yokohamashi Tobu Hospital. Results: Twenty-nine patients (19.9%) were diagnosed with delirium. Patients who were >70 years were divided into a delirium group (n = 24) and a non-delirium group (n = 41). Multivariate analysis showed that only the Charlson Age Comorbidity Index (CACI) (OR 1.8; 95% CI 1.067-3.036; p = 0.028) was an independent risk factor of delirium for patients >70 years. The receiver operating characteristic curve revealed an optimal cutoff value of 4.5 for the CACI score in all patients (sensitivity 62.1%; specificity 82.9%; area under the curve 0.782). The higher CACI score (≥5) is significantly different from the lower CACI score (p < 0.0001) with respect to POD occurrence. Conclusions: The CACI, especially in elderly patients, was associated with the incidence of POD. Therefore, utilizing this validated and practical tool preoperatively might be useful for POD.