The purpose of this study was to assess the variability of measuring the mitral valve area (MVA) by the cardiac catheterization (Gorlin) method and two Doppler echocardiographic methods, the pressure half-time and continuity equation methods. The determinants of MVA were measured simultaneously before and after percutaneous mitral balloon valvuloplasty (PBMV). Thirty-three patients with severe mitral stenosis underwent simultaneous measurements of MVA by the three methods immediately before and within 15 minutes after PBMV. After combining all data, the correlation between the catheterization and pressure half-time methods was significant (r = 0.65; p < 0.001), as was that between the catheterization and continuity equation methods (r = 0.64; p < 0.001). However, there was a large degree of variability among the measurements with the three techniques. The mean difference between the catheterization and pressure half-time methods of measuring MVA before PBMV was -0.2 +/- 0.4 cm2 and 0.1 +/- 0.3 cm2 between the catheterization and continuity equation methods. This variability was even more marked after PBMV: -0.5 +/- 0.9 cm2 between the catheterization and pressure half-time methods and 0.4 +/- 0.6 cm2 between the catheterization and continuity equation methods. Although previous studies have shown a good correlation between MVA as measured with the catheterization and two Doppler echocardiographic methods, they included a wide range of MVAs. In our study of patients with hemodynamically significant mitral stenosis, there was a large degree of variability between the catheterization and simultaneously performed Doppler echocardiographic methods. The calculated MVA by any method should not be used as the single measure of severity of stenosis.