A 72-year-old man was admitted to our hospital for acute back pain. Transesophageal echocardiography (TEE), computed tomography (CT) and magnetic resonance imaging (MRI) all showed the presence of intramural hematoma (IMH) located in the descending aorta, with bilateral pleural effusions. The patient was initially referred for medical therapy and 'watchful waiting'. However, he continued to have back pain, so we decided to perform invasive aortography examination and intra-aortic ultrasound (IAU) imaging. No penetrating aortic ulcer (PAU) was found on multiple angiographic views, but intra-aorta ultrasound imaging clearly showed a PAU measuring 3x1 mm(2) in connection with the intramural hematoma. Even retrospective analysis of CT images failed to reveal this PAU. Therefore, we think that IAU imaging may be a useful tool in the diagnosis of PAU.