In order to analyse the results of conservative mitral valve surgery in the treatment of mitral regurgitation due to infective endocarditis, the authors reviewed the cases of 48 patients operated between 1974 and April 1993 (36 operations having been performed after 1989, a period during which only 3 patients underwent mitral valve replacement for the same indication). Thirty-four patients were operated after sterilisation of the infective endocarditis, and 14 patients were treated during the active phase. There were 32 men and 16 women with an average age of 45 +/- 13 years. In two thirds of the cases, the causative organism was a streptococcus. Half of the patients were operated during the acute stage because of their poor haemodynamic status, 5 because of residual bacterial vegetations after one or more embolic events and two because of the infection itself. On the other hand, patients were operated after the infective phase because of severe mitral regurgitation, responsible for severe symptoms (NYHA Class III) in 16 cases. From the anatomical point of view, the peroperative finding of 14 patients operated in the acute phase included dilatation of the annulus (N = 9), ruptured chordae (N = 9), perforation (N = 8) or vegetations (N = 8); in the patients operated later, the incidence of perforation and vegetations was much lower (20%) whereas dilatation of the annulus was almost constant (91%).(ABSTRACT TRUNCATED AT 250 WORDS)