To evaluate the prevalence and clinical significance of echo-free space (EFS) in aortic intramural hematoma (AIH) during transesophageal echocardiography (TEE), TEE performed during the acute phase in 71 consecutive patients with type B AIH was reviewed. Forty-four patients (62%) had EFS including 24 patients with a large EFS occupying >1/2 of the hematoma thickness. Among 59 patients who also underwent computed tomography, focal contrast enhancement in the hematoma area was observed in only 7 patients with a large EFS. Hospital mortality and incidence of surgical intervention in patients with EFS were 0% and 2%, respectively, which was similar to 4% in those without EFS. Follow-up imaging studies in 57 patients (80%) revealed development of typical aortic dissection (AD) in 6 patients and complete resorption of hematoma in 35; the incidence of either the development of AD or a complete resorption of hematoma was not significantly different between those with and without EFS. EFS by TEE is not rare in patients with type B AIH. It is not a poor prognostic factor and is not associated with the development of AD.