A very rare case of tricuspid valve endocarditis which developed in a healthy adult was observed. An 18-year-old man with no history of heart disease nor use of stimulant drugs was diagnosed as having cardiac tumor, introduced to this hospital and admitted. Before the operation, symptoms characteristic to infective endocarditis such as high fever and embolism were not observed, but the tumor was detected in the right ventricle by echocardiography. The patient underwent cardiotomy. The thrombus was removed and annuloplasty was performed by Kay's method, and good results were obtained. Pathologically the disease was diagnosed as infective endocarditis accompanied by thrombus. The postoperative course has been good. When the injury of the valve is slight, the surgical method preserving patient's own valve such as excision of localized vegetation and annuloplasty appears to be useful.