Magnetic resonance imaging (MRI) improves our ability to assess brain development and to detect anomalies of brain formation. MRI allows the assessment of brain development by analysis of the effects of myelination on the T1 and T2 relaxation times of the pediatric brain. This article discusses specific imaging strategies and the normal progression of signal intensity changes. Familiarity with this evolution of signal changes allows an estimation of the approximate stage of brain development. High-resolution multiplanar MRI provides good anatomic detail, with excellent distinction between gray and white matter. This technique allows improved detection of many classes of abnormalities of brain formation, some of which were previously detectable only at autopsy. These malformations and their imaging characteristics are discussed under the headings of: corpus callosal dysgenesis, intracranial lipomas, holoprosencephalies, septooptic dysplasia, the cephaloceles, the Chiari malformations, the Dandy-Walker complex, the cerebellar anomalies including Joubert's syndrome, and rhombencephalosynapsis, and the spectrum of neuronal migration anomalies.