A 21-year-old man who had a history of intravenous drug addiction was admitted with complaints of high fever and a productive cough. Chest CT on admission showed multiple consolidations, and pneumonia was initially diagnosed and treated. Because echocardiography after admission showed vegetation, with no bacteriological findings, attached to the tricuspid valve, right-sided infective endocarditis was diagnosed. After antibiotic therapy was changed, his fever was reduced and the inflammatory findings were eliminated. In the western world, most cases of right-side infective endocarditis are caused by drug addicts, but in Japan, this disease is very rare. Right-side infective endocarditis in drug addicts causes a high rate of pulmonary complications, in particular, septic pulmonary embolism. Many drug addicts suffering from pulmonary complications may consult doctors, but if the latter are not well-informed about this disease, it may not be possible to give an accurate diagnosis or proper treatment.