PURPOSE--To study characteristics of the natural history of mitral stenosis (MS) in patients that have no correlation between mitral valve areas (MVA) and symptoms. METHODS--We studied 18 patients with MS, that presented no correlation between MVA and functional class (FC), 16 (89) were female and two (11) men, with age ranging from 16 to 54 (mean 33) years. Patients assigned to group A (8 cases) had FC III and MVA > or = 1.5 cm2 and group B (10 cases) FC I/II and MVA < 1.1 cm2. FC and MVA at the start (initial time-It) and after 12 months or before surgical correction (SC) or percutaneous mitral balloon valvuloplasty (PBV) (final time-Ft) were compared. All patients with predict O2 uptake (PRED VO2) at It were evaluated. RESULTS--Five (63) patients of group A, that maintained MVA > or = 1.5 cm2, changed to FC I/II but three (38) needed a SC or PBV (2 with lesser MVA at Ft). At group B, six (60) patients needed SC or PBV. CONCLUSION--MS patients with MVA > or = 1.5 and FC III, providing MVA do not decrease, improves their FC, becoming it more compatible with MVA PRED VO2. The cases of group B presented the greatest probability of needing SC or PVB.