Conservative surgery for non-av-canal mitral valve anomalies was performed in 30 children under 15 years of age between 1965 and 1986 at our institution. In 14/30 (47%) children these anomalies were isolated (without other intra- or extracardiac defects). Mean age of the 14 children was 6.7 years (range 9 months to 15 years). Preoperatively mitral insufficiency was found in 12 cases, stenosis in one and combined insufficiency and stenosis in one case. The following morphological substrates of mitral valve were found: annular dilation 3, leaflet anomalies 20, chordal anomalies 4, papillary muscle anomaly 1. Surgical technique was as follows: annuloplasty 9, plication of leaflet 4, closure of cleft 10, commissurotomy 2, displacement of papillary muscle 1. Early mortality was 1/14 (7%) patients. There was no death during a mean follow-up interval of 14.8 years (range 30 days to 25 years). Actuarial survival was 93% after 10 and 15 years (95% confidence limits 78-100%). A total of 2 reoperations was necessary (delay 16 day and 46 months). In both cases valve replacement was performed (valve size 27 and 29 mm). Actuarial reoperation-free interval was 77% after 10 and 15 years (95% confidence limits 53-100%). In conclusion conservative surgery for isolated mitral valve disease gives good long-term results. When reoperation is necessary, adult-sized prosthesis can be implanted. Conservative surgery is the procedure of choice for congenital mitral valve disease.