Most pneumonia-related researches in people with severe mental illness were based on insurance claims data. This study aimed for a comprehensive analysis of factors potentially associated with risk of pneumonia in psychiatric inpatients.Inpatients at a large psychiatric hospital diagnosed with pneumonia during the course of hospitalization were enrolled as cases. Controls were matched by ward and date. The diagnosis of pneumonia was confirmed by physicians based on clinical features, chest radiographs, and blood tests. A stepwise conditional logistic regression model was used to identify potential risk factors for pneumonia.Seventy-five pneumonia cases and 436 matched controls were enrolled. Conditional logistic regression revealed 3 variables significantly associated with an increased risk of pneumonia: a higher score on the Clinical Global Impression-Severity scale (adjusted odds ratio [aOR], 3.7; 95% confidence interval [CI]. 1.5-9.1), a higher score on the Charlson comorbidity index (aOR, 2.2; 95% CI, 1.5-3.2), and a longer duration of antipsychotic treatment (aOR, 1.0; 95% CI, 1.0-1.0). Two variables were significantly associated with a decreased risk of pneumonia: a higher score on the Global Assessment of Functioning scale (aOR, 0.9; 95% CI, 0.8-0.9) and an older age of onset (aOR, 0.9; 95% CI, 0.9-1.0). After adjusting for potential confounders, use of antipsychotic or other psychotropic medications was not found to be a significant risk factor for pneumonia.Physical comorbidities, long duration of antipsychotic treatment, early onset, severe psychiatric symptoms, and poor global functioning are associated with pneumonia in people with serious mental illness.