Postmortem examination of a 43-yr-old male southern white rhinoceros (Ceratotherium simum simum) revealed gross lesions and histopathologic findings consistent with endocarditis. The animal was born in Umfolozi National Park, South Africa, and then it was moved at 2 yr of age to two successive European zoologic collections. For several weeks prior to death, the animal was increasingly recumbent or assuming a dog-sitting position. Postmortem examination revealed cutaneous pressure sores and multiple rough nodular structures on the mitral valve and left ventricular endocardium. Histopathologic examination revealed vegetative endocarditis, myocardial and hepatocellular degeneration, hepatic fibrosis, and chronic nephritis. Bacterial culture from the oral cavity, trachea, lung, skin, and heart isolated beta hemolytic Streptococcus dysgalactiae subsp. equisimilis and Streptococcus ovis. The cause of death was acute cardiopulmonary failure due mainly to endocarditis and moderate myocardial degeneration. Streptococcal infections are not uncommon causes of morbidity and mortality in rhinoceros. This is the first detailed report of streptococcal endocarditis in a rhinoceros.