Objective: To identify characteristics associated with complications during pregnancy in patients with mitral stenosis. Methods: Thirty-seven pregnant women with mitral stenosis, followed-up from 1998 to 2001 were evaluated. Predictor variables were the mitral valve area (MVA) measured by echocardiogram and functional class (FC) before pregnancy according to NYHA criteria. Progression of functional class, thromboembolism, death, need in medical abortion, cardiac surgery or balloon mitral valvulotomy were accepted as maternal events. Fetal/neonatal events were determined as abortion, fetal or neonatal death, prematurity or low birth weight (<2.500g), and extended stay in the nursery or hospitalization in newborn intensive care unit. Results: The mean ± SD of age of the patients was 24.7±5.8 years. The eventful and uneventful patients were similar in age and percentage of first pregnancies. Of patients with an events occuring during gestational period, 37. 5% had class I functional capacity whereas 62.5% had class II/III (p=0.001). A clinical event was noted in 34 % of the patients with sinus rhythm and in all of patients with atrial fibrillation (p=0.007). The mean mitral valve area was 1.11±0.23 cm2 in the group with clinical event and 1.6±0.27 cm2 in the group without an event (p<0.001). The most frequently observed maternal complication was the worsening of the functional capacity and the most frequent fetal/neonatal complications were prematurity and low birth weight. Mitral valve area and functional capacity were found to be significantly related with maternal complications but not with the fetal/neonatal complications. Conclusion: In pregnant women with mitral stenosis, the MVA and the FC are strongly associated with maternal complications but not related to fetal/neonatal events.