PURPOSE: The clinical evolution of women with mitral stenosis was studied during pregnancy, delivery and puerperium in initial function (FC) class I/II. METHODS: Ninety-three women were divided in three groups: Group GE--Pregnant women with mitral stenosis (n = 30, mean age 28 years); 26 (86.7%) patients had electrocardiographic signs of left atrial enlargement and nine (30%) had signs of right ventricular hypertrophy. The mitral valvar area was between 0.7 and 1.9 (mean = 1.26) cm2 at echodopplercardiogram; Group GM--Normal pregnant women (n = 32; aged 25.4 years); the electrocardiogram and echodopplercardiogram were normal. Group EM--non pregnant patients, with mitral stenosis (n = 31.33 years); 19 (61.3%) had left atrial enlargement and four (13%) had right ventricular hypertrophy. The mitral valvar area between 0.50 and 1.80 (mean = 1.19) cm2. The variables analyzed were FC and occurrence of the following complications: infective endocarditis, cardiac arrhythmias and thromboembolism. RESULTS: In GE group, 26 (86.7%) patients worsened the FC during gestation, 16 to FC III and 10 to FC IV. In GN group, 18 (56.2%) patients changed from FC I to FC II during the gestation and in EM group 5 (16.2%) patients changed from FC I/II to III during the study. Cardiac arrhythmias and infective endocarditis were not observed; thromboembolic event was registered in one (3.2%) patients from EM group. There were no death in all groups. CONCLUSION: The large majority of pregnant with mitral stenosis that started pregnancy in FC I/II worsened to FC III/IV during gestation. Medical treatment and eventually balloon valvuloplasty were successful measure to allow a full-term gestation without mortality.