The purpose of this study was to define the contribution of transesophageal echocardiography to the diagnosis of right atrial tumors in a large series of patients with this rare finding. Transesophageal echocardiography (TEE) has been found to be valuable in evaluating patients with intracardiac masses and has been shown to be superior to transthoracic echocardiography (TTE) in evaluating left heart masses. Between 1989 and 1993, 23 patients with either known tumors elsewhere or right atrial masses that were detected on TTE were evaluated with TEE. TEE studies were performed in the noninvasive cardiology laboratory. All patients were studied with 5 MHz biplane or omniplane transducers. The right atrium was evaluated for the presence, characteristics, extent, and attachment of any masses and for extension of these masses into the great vessels or other cardiac chambers. No complications occurred. Six patients had primary right atrial tumors. In 10 patients the tumors reached the right atrium via the inferior vena cava. Seven patients had malignant secondary tumors. TEE demonstrated three tumors not detected by TTE. Furthermore TEE provided 16 additional findings not seen on TTE. In conclusion, TEE is superior to TTE in the evaluation of right atrial tumors. TEE should be considered in patients with right atrial tumors even when these tumors have been demonstrated with TTE.