Seventy-eight consecutive episodes of infective endocarditis on native valves have been prospectively treated and followed-up after discharge from 1975 to 1982 (mean follow-up period 31 months). Twenty one patients needed valvular replacement in the active phase of the disease. Overall mortality was 15 cases, 7 from the medical group and 8 from the surgical group. At last clinical control 21 from the 46 survivors of the medical group remained asymptomatic, 17 had needed valvular replacement, 5 had died 2 of congestive heart failure and 3 (addicts) were lost to follow-up. From the 13 survivors of the surgical group 8 remained asymptomatic with good prosthetic function, 4 had needed reoperation due to severe periprosthetic leak and 1 died suddenly during follow-up. Figures at the end of follow-up showed that 28% of the initial patients had died, 39% carried a valvular prosthesis and 28% remained asymptomatic. A retrospective analysis of factors predictive of poor prognosis has been carried out.