In a retrospective analysis of bacterial endocarditis, 84 of 192 cases (44%) were found to have musculoskeletal manifestations of one or more types. Common manifestations were arthralgias (32 cases), arthritis (26 cases), low back pain (24 cases), diffuse myalgia (16 cases), and myalgias localized to the thigh or calf (11 cases). The joint manifestations typically were monarticular or oligoarticular, and the myalgias were commonly unilateral. No association was found between the pattern of rheumatic symptoms and other clinical manifestations, laboratory tests, or causative bacterial organisms. In 52 patients (27%), musculoskeletal complaints were the first or among the first symptoms of bacterial endocarditis. The frequency and character of these manifestations and their tendency to occur early in the course of the disease indicate that they are an important feature of endocarditis which, if not recognized, may cause a delay in the diagnosis by mimicking a rheumatic disease.