To determine the value of transesophageal ultrasound in the assessment of patients after percutaneous mitral valvuloplasty, 42 patients were studied by transthoracic (TTE) and transesophageal (TEE) two-dimensional and color Doppler echocardiography. All of them were studied as out-patients and without complications. We describe the technique, planes of examination and the advantages that this new acoustic window offers in patients after balloon valvuloplasty regarding to: detection of thrombus in the left atrium (LA), visualization of spontaneous echo contrast in the LA, evaluation of mitral regurgitation (MR), detection of small atrial septal defects (ASD) and evaluation of the stage of the commissures of the mitral valve. We detected thrombus by TEE, in 5/42 vs 1/42 by TTE approach. Spontaneous echo contrast was found in 35/42 by TEE and none by TTE. Small ASDs were visualized in 10/42 patients vs 2/42 by TTE. No differences were found in the evaluation of MR and mitral valve commissures either by TEE or TTE. We conclude that transesophageal echocardiography is a well-tolerated technique in outpatients which complements and improves the information obtained by the transthoracic approach in patients after balloon mitral valvuloplasty.