Patients with oral and maxillofacial malignant tumours have a relatively high incidence of postoperative infections. We have analysed the risk factors and the distribution of pathogens in infected patients to try and find out how to prevent them. We recruited 312 patients over 60 years old with malignant oral and maxillofacial tumours and investigated their incidence of postoperative infection between January 2007 and December 2017. Some factors were included in one way and multifactorial logistic analyses to find out which risk factors were likely to be associated with postoperative infections. Thirty-nine of the 312 (12.5%) developed postoperative infections, mainly at the surgical site (n = 21) and in the lower respiratory tract (n = 14). Pathogens were isolated from all patients and comprised aerobic (n = 4) and anaerobic (n = 5) bacteria, together with mixed infections (n = 30). Univariate analysis showed that age, size and site of tumour, body-mass index (BMI), diabetes, and duration of operation were risk factors. Multivariate logistic analyses, however, showed that BMI, the presence of diabetes, duration of operation, and American Society of Anesthesiologists (ASA) score were the main independent risk factors for postoperative infection. We conclude that there are abundant risk factors for postoperative infection in these patients, and it is important that they are evaluated preoperatively so that suitable postoperative treatments can be given. (C) 2019 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.