Transthoracic echocardiography is useful for evaluation of the coronary arteries in infants and children with Kawasaki disease. In adults, however, transthoracic echocardiography often cannot detect or accurately estimate coronary artery lesions. We describe two young adults admitted for a diagnosis of acute myocardial infarction ascribed to Kawasaki disease and treated by angioplasty. Coronary aneurysms were not evident in either patient at the time of angioplasty. However, follow-up transthoracic echocardiography revealed coronary aneurysms at the culprit lesions. On follow-up angiograms, we identified a new coronary aneurysm in the first patient, and a regressed coronary aneurysm in the second, confirmed by intravascular ultrasound imaging. These cases suggest that transthoracic echocardiography plays an important role in the diagnosis and treatment of young adults with acute myocardial infarction due to Kawasaki disease.