Background: Methods: This retrospective cohort study was conducted in 3 hospitals in an urban region of Southern California. The sample included adult patients with empyema and pleural fluid cultures positive for 1 or more SAG microorganisms. We excluded patients with bronchopleural fistulas or lung abscess because SAG bacteria are known to be a cause of those infections and can breach the physical barrier of the visceral pleura. Results: Thirty-seven patients with SAG empyema were identified: 14 had had polymicrobial cultures including 1 or more species of SAG bacteria (pSAG) and 23 had pure cultures of SAG bacteria. The patients were mostly middle-aged men with comorbidities, some of which predispose to aspiration or the inability to clear aspirated secretions. The patients with pSAG empyema were more likely to have cancer and/or prior surgical disruption of the esophagus with resulting mediastinitis. Patients with SAG empyema were more likely to use substances such as alcohol, sedatives, and narcotics. All computed tomography (CT) scans were initially interpreted as atelectasis abutting the empyema, but 13 patients with SAG empyema had contrast-enhanced CT scans that were suitable for measuring Hounsfield units (HUs) in the areas of consolidation adjacent to the SAG empyema; these scans revealed that they all had pneumonia as the source of their empyema. The most common species isolated from the SAG cases was Conclusions: Community-acquired SAG empyema is a complication of unrecognized SAG pneumonia.