OBJECTIVE: To evaluate the effectiveness and safety of percutaneous balloon mitral commissurotomy for the treatment of pregnant women with severe mitral stenosis over a period of six years. DESIGN: Analysis of clinical, haemodynamic, and echocardiographic data before and immediately after the procedure, the pregnancy outcome, and the fate of newborn babies. SETTING: Academic cardiovascular centre in Monastir, Tunisia. PATIENTS: 44 pregnant patients who underwent percutaneous transvenous dilatation of the mitral valve between January 1990 and February 1996. Grade 2 mitral regurgitation was present in two patients and densely calcific valves in three (7%). RESULTS: Commissurotomy was successfully achieved in all cases. The total mean (SD) duration of teh procedure was 72 (18) minutes and that of fluoroscopy 16 (7) minutes. Left atrial pressure decreased from 28 (10) to 14 (7) mm Hg, mitral pressure gradient fell from 22 (8) to 5 (3) mm Hg. Cardiac output increased from 4.8 (1.1) to 6.3 (1.2) l/min and Gorlin mitral valve area from 0.96 (0.21) to 2.4 (0.4) cm2 (all P < < 0.001). Cross sectional echocardiographic mitral valve area increased from 1.07 (0.21) to 2.32 (0.36) cm2. There were no maternal or fetal deaths. Complications included a grade 4 mitral regurgitation in one patient that required early valve replacement. All patients delivered at full term, 42 vaginally and two (5%) by caesarean section; 41 babies were normal and three whose mothers had the procedure near term were relatively hypotrophic. At a mean follow up of 28 (12) months (range 2 to 26) all children had normal growth. CONCLUSIONS: During pregnancy, balloon mitral commissurotomy is the treatment of choice of severe pliable mitral stenosis in patients who are refractory to medical treatment.