Lungs and lymph nodes of 79 Atlantic bottlenose dolphins (Tursiops truncatus) that died from 6 August 1987 to 16 April 1988 along the Atlantic coasts of New Jersey, Virginia, and Florida (USA) were examined histologically and were tested for the presence of morbillivirus antigen by an immunoperoxidase technique. Lung lesions included areas of interstitial pneumonia characterized by varying combinations of type II pneumocyte hyperplasia, interstitial fibroplasia and leukocytes, syncytia, and intranuclear and intracytoplasmic inclusion bodies. Fungal, bacterial, and mixed bacterial and fungal pneumonias were common. Lymphoid depletion, lymphocytosis, syncytia, and intranuclear and intracytoplasmic inclusion bodies were present in lymph nodes. Morbillivirus antigen was detected in 42 (53%) of 79 dolphins examined. Based on histopathologic and immunocytochemical findings, we diagnosed morbillivirus-induced disease. This is the first report of disease caused by morbillivirus in bottlenose dolphins and in any cetacean species outside Europe.