Three cases of endocarditis confirmed at autopsy were identified in an intensive care nursery during an eight-month period. Echocardiography demonstrated abnormal echoes in the region of the mitral valve in one infant and the tricuspid valve in the other two infants. Both the diverse clinical manifestations of bacterial and nonbacterial endocarditis and the value of echocardiography in the establishment of an antemortem diagnosis are discussed. This previously unusual entity seems to be occurring with greater frequency in neonatal intensive care units that provide vigorous efforts to support severely ill infants.