Purpose: Community-acquired pneumonia (CAP) is highly common across the world. It is reported that over 90% of CAP in older adults may be due to aspiration. However, the diagnostic criteria for aspiration pneumonia (AP) have not been widely agreed. Is there a consensus on how to diagnose AP? What are the clinical features of patients being diagnosed with AP? We conducted a systematic review to answer these questions. Methods: We performed a literature search in MEDLINE^®, EMBASE, CINHAL, and Cochrane to review the steps taken toward diagnosing AP. Search terms for “aspiration pneumonia” and “aged” were used. Inclusion criteria were: original research, community-acquired AP, age ≥ 75 years old, acute hospital admission. Results: A total of 10,716 reports were found. Following the removal of duplicates, 7601 were screened, 95 underwent full-text review, and 9 reports were included in the final analysis. Pneumonia was diagnosed using a combination of symptoms, inflammatory markers, and chest imaging findings in most studies. AP was defined as pneumonia with some relation to aspiration or dysphagia. Aspiration was inferred if there was witnessed or prior presumed aspiration, episodes of coughing on food or liquids, relevant underlying conditions, abnormalities on videofluoroscopy or water swallow test, and gravity-dependent distribution of shadows on chest imaging. Patients with AP were older, more frailer, and had more comorbidities than in non-AP. Conclusion: There is a broad consensus on the clinical criteria to diagnose AP. It is a presumptive diagnosis with regards to patients’ general frailty rather than in relation to swallowing function itself.