Purpose: Agent Orange (AO) is a herbicide and defoliant used by the United States and its military allies during the Vietnam War. Pneumonia is a common cause of death among Vietnam veterans in our hospital. There have been no previous studies researching any association between AO exposure and the prognosis for pneumonia. The primary objective of this study was to investigate associations between AO exposure and 30-day mortality due to pneumonia. The secondary objective was to examine the clinical factors associated with therapeutic outcomes in veterans with pneumonia, and to assess the prevalence of combined diseases in AO-exposed veterans. Methods: This study retrospectively included veteran patients diagnosed with pneumonia in the emergency department and hospitalized between February 2014 and March 2018. The enrolled patients were grouped according to their defoliant exposure history, and the clinical information of defoliant-exposed and non-defoliant-exposed groups were compared. Patients were divided according to 30-day mortality, and significant factors influencing mortality were evaluated by using univariate analysis and multivariate analysis. The final multivariate model revealed the effect of AO exposure on therapeutic outcomes of pneumonia. Results: A total of 1006 patients were analyzed. Of these, 276 patients had a history of AO exposure, whereas 730 patients had not been exposed. Factors positively associated with 30-day mortality were malignancy, respiratory rate, blood urea nitrogen, and albumin which was negatively associated with mortality. Conclusion: Exposure to defoliant is not associated with 30-day mortality in patients with pneumonia. However, veterans with defoliant exposure are associated with a high prevalence of diabetes mellitus, hypertension, cerebrovascular accident, malignancy, and chronic kidney disease.