We present a case of the infant form of Alexander disease. The case uniqueness is that the patient’s examination had been started at the preclinical stage and was continued during the manifestation and fastigium of disease. We present rare images obtained during neurosonography at the preclinical stage of the disease as well as the unique findings of MRI studies. The MRI findings at disease onset and 3 years later indicate that the infant form of Alexander disease is characterized by clinical stages.