A consecutive series of 130 cases of pure or predominant mitral regurgitation underwent conservative mitral valve surgery between January 1975 and January 1982. The mean age of the patients was 30 +/- 17 years; 25 patients were under 15 years of age. The most common aetiology was rheumatic fever (112/130). Fifty nine patients had associated valvular lesions requiring surgical correction. The patients were divided into 4 groups, according to the surgical technique: Group I: valvular mobilisation (35 cases); Group II: reduction of the amplitude of valvular excursion (48 cases); Group III: mixed valvular mobilisation and reduction of amplitude of excursion (45 cases); Group IV: isolated annuloplasty (2 cases). Hospital mortality was 2.3% (3 patients). Five patients (3.8%) were lost to follow-up. The mean follow-up period was 38 +/- 27 months for the 122 patients followed-up. Seven patients needed reoperation. The long term mortality was 3.1% (4 patients). Four late thromboembolic episodes were observed; they were all transient and regressive in patients with atrial fibrillation. The 7 year actuarial survival rate for the whole series, including hospital mortality, was 92% (1.0 +/- 0.5 patients/year). It was 93.7 +/- 4.9% at 7 years for isolated mitral valvuloplasty and 89.9% +/- 5.6% at 5 years for combined mitro-tricuspid procedures. The actuarial percentage of patients without thromboembolic complications was 91.2% at 7 years with a thromboembolic risk of 1.0 +/- 0.5% patients/year. Eighty eight per cent of patients were not reoperated at 7 years and the reoperation rate was 1.7 +/- 0.7% patients/year.(ABSTRACT TRUNCATED AT 250 WORDS)