Unlike atrophy of the corpus callosum (CC), callosal hypertrophy is a rare neuroimaging finding with only few reported patients. The "megalencephaly, mega CC, and complete lack of motor development" syndrome is morphologically characterized by generalized megalencephaly, a thickened CC, and extensive polymicrogyria causing a pachygyric appearance. We report on the fifth patient showing this rare syndrome, a 3-year-old girl displaying the typical neuroimaging features. Clinically she showed a severely impaired motor, mental, and speech development with marked muscular hypotonia but no dysmorphic facial signs. She also retained the ability to move by rolling sidewards so that complete lack of motor development may not be a consistent feature.