Background: Head and neck cancers (HNCs) and their treatment may cause oral function impairment. Purpose: This study was designed to identify oral dysfunction in patients receiving treatment for HNCs using a systematic review. Methods: The PubMed, Embase, and CINAHL databases were searched for studies on oral function impairment in patients receiving treatment for HNCs published between January 2014 and May 2019. Only descriptive, correlational, and interventional quantitative studies that included patients receiving treatment for HNCs who presented with oral dysfunction, were published in English during the aforementioned time frame, and were accessible in full-text versions were selected. Results: Twenty-eight studies (13 cross-sectional, two longitudinal, 12 randomized controlled trial, and one retrospective chart review) fulfilled the inclusion criteria. Oral mucositis, dysphagia, xerostomia, trismus, and chewing and speech problems were the most common oral dysfunctions. Age, cancer stage, tumor location, treatment modalities, treatment status, treatment dose, and pretreatment oral function were factors associated with oral dysfunction. Although individual interventions were shown to improve oral dysfunction, the related evidence was inconclusive. Conclusions/Implications for Practice: Primary HNCs and their treatment significantly deteriorate oral function. A holistic and interdisciplinary approach may maximize oral function.