Pneumonia is one of the most common causes of morbidity in bottlenose dolphins Tursiops truncatus. To better understand associations of pneumonia with demographics, microbiology, pathology, and histopathology, a retrospective study on 42 dolphins from the US Navy Marine Mammal Program dolphin population was conducted (1980 to 2010). A total of 21 (50%) of the dolphins evaluated had pneumonia confirmed by histopathology. Bacterial and fungal pneumonia was present in 42.9 and 28.6% of cases (9 and 6 cases), respectively, with Staphylococcus aureus as the most common confirmed pathogen (4 cases, 19%). Other pathogens identified as the cause of pneumonia were Cryptococcus neoformans, Erysipelothrix rhusiopathiae, Histoplasma capsulatum, parainfluenza virus, Proteus species, Pseudomonas aeruginosa, and Streptococcus zooepidemicus. Neither sex nor age was a predictor of pneumonia. While many of the infections involved disseminated disease, lungs were consistently the most severely affected organs. The present study demonstrates the high susceptibility of dolphins to respiratory infections. Areas that warrant further investigation include eosinophilic pneumonia, chronic infections, co-infections, and metabolic or iron-storage diseases. There is a continuing need to improve the early diagnosis and effective treatment of pneumonia in dolphins.