A 6-month-old female infant was diagnosed with Leigh syndrome after an abnormal muscle specimen was obtained and after magnetic resonance imaging demonstrated characteristic cranial lesions. She presented with episodic hyperventilation, myoclonus, ophthalmoplegia, hypotonia, and elevation of lactate in the cerebrospinal fluid and blood. A series of cranial ultrasounds revealed progressive ventricular enlargement before the typical lesions were detected by magnetic resonance imaging. Myelin destruction is believed to play an important role in the early stage of Leigh syndrome. Ultrasonography may provide a convenient way to document changes in brain that provide early suspicion of Leigh syndrome.