Recognizing the progression of myelination in normal brain development is critical for detecting white matter diseases of childhood. The cholesterol content of myelin is responsible for the high SI appearance of white matter on T1WI. Thus, the MRI SI relationship between gray and white matter in neonates—in whom the latter is not yet myelinated—is reversed. Myelination begins in the occipital lobe, centrum semiovale, internal capsule, and corpus callosum and is best assessed with T1WI. Myelination progresses from central to peripheral, posterior to anterior, and from sensory to motor tracts. By one year of age, T1WI demonstrates close to the adult pattern of gray and white matter SI. As the water content of newly formed myelin progressively decreases, the SI of white matter on T2WI declines, with marked changes occurring between 1 and 2 years of age (at which time the appearance is close to that of the adult pattern). Terminal areas of myelination—the white matter of the parietal lobes surrounding the ventricular trigones—may demonstrate high SI on T2WI up until 10 years after birth.