To evaluate the usefulness of transesophageal echocardiography (TEE) in the treatment of critically ill patients, 80 patients (51 male and 29 female; mean age, 53 years) undergoing both transthoracic echocardiography (TTE) and TEE were studied in a 2-year period. Of these, 48 patients were studied in the ICU, while the other 32 patients were directly referred from the emergency departments. Indications for the study included suspected aortic dissection (34 patients), hemodynamic instability (22 patients), suspected cardiac source of embolism (11 patients), evaluation of the severity of mitral regurgitation (7 patients), and suspected infective endocarditis (6 patients). The probe was passed successfully in 78 of 80 attempts (98 percent). No significant complications were recorded during the transesophageal echocardiographic study. Transesophageal echocardiography provided critical information that was not obtained by TTE in 39 of 78 studies (50 percent, p < 0.005). Cardiac surgery was prompted by TEE findings in 14 patients (18 percent) and these findings were all confirmed at operation. Transesophageal echocardiography was a safe, well-tolerated, and valuable diagnostic approach for the rapid detection of specific cardiac abnormalities in patients with critical illness; TEE should be considered in the treatment of critically ill patients especially when TTE provided inadequate information.