The authors report a new case of primitive isolated endocarditis of the tricuspid valve. The microorganism responsible, Streptococcus sanguis, is unusual in its localization and in this environment. The uncomplicated evolution poses the problem of deciding what action should be taken vis-à-vis the persistence of an important isolated vegetation after effective antibiotic treatment. Therapeutic abstention was chosen rather than surgical intervention in light of the literature. A spontaneous pulmonary embolic migration of the vegetation was effectuated 3 weeks after termination of the antibiotic treatment without pulmonary or hemodynamic complications.