From 1975 to 1988 we have operated 117 patients with left arterial thrombosis associated with rheumatic mitral valve disease. Seventy-seven were female and 40 male, with ages ranging from 22 to 69 years. In 75 cases (64.1%) the valvular lesion was mitral stenosis. Embolic antecedents were present in 38 cases (32.4%) and 95 patients (81.1%) were in class III or IV of the NYHA functional classification. In 48 cases we performed a mitral commissurotomy and in 51 cases mitral valve replacement, associated to left artrial thrombectomy. In the remaining 18 patients we made other valve procedures. The hospital mortality was 15 cases (12.8%), eight because low cardiac output, four because severe brain injury and three because posterior atrioventricular sulcus disruption. In 41.1% of the survivors there was serious hospital complications, standing out the incidence of 8 cases of transient neurologic accidents. We have followed 98 of the 102 hospital survivors between 10 and 140 months (mean 57 months). Three patients died in the follow-up, two of them during a reintervention because bioprosthesis disfunction and the third one during a reintervention because prosthetic infective endocarditis. Nine additional patients were reoperated because recidivant valvular lesions or because prosthetic disfunction, and two patients suffered embolic events during the follow-up. The antithrombotic therapy was abandoned in 19.6% of patients. At present 73.6% are in functional class I and 26.3% in class II. The association of left atrial thrombosis with with mitral valve disease induce a surgical morbimortality greater than usual for isolated valvular lesions, being mandatory a watchfull surgical technic.(ABSTRACT TRUNCATED AT 250 WORDS)