Oropharyngeal dysphagia is a common condition after stroke, Parkinson's disease (PD), and Alzheimer's disease (AD), and can cause serious complications including malnutrition, aspiration pneumonia, and premature mortality. Despite its high prevalence among the elderly and associated serious complications, dysphagia is often overlooked and under-diagnosed in vulnerable patient populations. This systematic review aimed to improve understanding and awareness of the prevalence of dysphagia in susceptible patient populations. MEDLINE, EMBASE, the Cochrane library, PROSPERO, and disease-specific websites were systematically searched for studies reporting oropharyngeal dysphagia prevalence or incidence in people with stroke, PD, AD, traumatic brain injury, and community-acquired pneumonia, from the USA, Canada, France, Germany, Italy, Spain, UK, Japan, China, and regional studies. The quality of study descriptions were assessed based on STROBE guidelines. A total of 1207 publications were identified and 33 met inclusion criteria: 24 in stroke, six in PD, two in traumatic brain injury, and one in patients with traumatic brain injury. Dysphagia was reported in 8.1-80 % of stroke patients, 11-81 % of PD, 27-30 % of traumatic brain injury patients, and 91.7 % of patients with community-acquired pneumonia. No relevant studies of dysphagia in AD were identified. This review demonstrates that dysphagia is highly prevalent in these populations, and highlights discrepancies between studies, gaps in dysphagia research, and the need for better dysphagia management starting with a reliable, standardized, and validated method for oropharyngeal dysphagia identification.