A 39-year-old female with a Hall-Kaster mitral prosthesis developed fever, general malaise and arthralgia 15 years after valve replacement for rheumatic mitral valve disease. Prosthetic valve endocarditis was identified after serial laboratory, clinical and echocardiographic examinations. Penicillin G (40 x 106 units/day, i.v.) + gentamicin (240 mg/day, i.v.) was started as initial therapy. The patient showed no signs of recovery, and penicillin G was replaced with vancomycin (1,000 mg/day, i.v.). There was a gradual reduction in spiking fever, and prominent reductions in erythrocyte sedimentation rate and white cell count. Meanwhile, a tender and pulsatile mass developed in the anterior surface of the left arm; peripheral angiography yielded a diagnosis of brachial artery aneurysm. A successful aneurysmectomy with saphenous vein interposition was performed. Histopathology of the lesion revealed mycotic aneurysm. An initial control SAT for Brucella of 1/80(+) was found to increase. A detailed history showed the patient to have consumed unpasteurized dairy products. Doxycyline (200 mg/day, oral) + co-trimoxazole (2,700 mg/day, oral) + rifampicin (600 mg/day, oral) was administered to treat brucellosis. Later, doxycyline caused intolerable gastrointestinal side effects and was replaced by ciprofloxacin (1,000 mg/day, oral). Subsequently, the patient made an uneventful recovery within one week. Antibiotic treatment was continued for 12 months, with complete resolution of vegetation and paravalvular leakage. During a four-year follow up, the patient showed no signs of relapse.