Objective: The aim of this study was to identify factors that are associated with the occurrence of pneumonia in patients with head and neck cancer (HNC) after treatment. Data Sources: PubMed, Scopus, OVID, and Cochrane Library from inception to November 26, 2019. Review Methods: A systematic review in accordance with the PRISMA guidelines and an assessment of bias were performed. Included studies reported on the risk factors of pneumonia development after HNC treatment via odds ratios and subdistribution hazard ratios from regression analysis. Results: Fifteen studies were included, comprising 30,962 patients with a mean age of 70 years (range, 19-95 years). Of these, 71.6% are male. The results of our study indicate that the following were independent risk factors contributing to the development of pneumonia: male sex, habitual alcohol consumption, poor oral hygiene before treatment, pretreatment dysphagia, hypopharynx and nasopharynx tumor sites, use of radiotherapy with or without chemotherapy versus surgery alone, addition of chemotherapy to radiotherapy, reirradiation, neck dissection, increased duration of tracheotomy, and use of sedatives for sleeping. Conclusion: Multiple patient-, tumor-, and treatment-specific risk factors were identified in predicting pneumonia. Recognition of these risk factors early on may help prevent or at least detect pneumonia in this vulnerable group of patients. [ABSTRACT FROM AUTHOR]