The natural history and prognosis of native valve infective endocarditis, prosthetic endocarditis and right sided endocarditis in drug addicts is analyzed. In native endocarditis mortality during the active phase is 12% and survival at 10 years 81%. Early prosthetic endocarditis has a worse prognosis. In late prosthetic valve endocarditis prognosis depends on the infective organism: mortality is less than 10% in estreptococcal infections and higher than 50% in staphylococcal infections. Right sided endocarditis in intravenous drug addicts has a relatively benign prognosis and seldom requires surgical treatment.