Sonography is a reliable tool for the evaluation of the most severe congenital abnormalities of the brain; in the present case it provided an early demonstration of hemimegalencephaly in hypomelanosis of Ito in a newborn affected by body hemihypertrophy and skin lesions. Serial magnetic resonance (MR) examinations confirmed the asymmetry of the cerebral hemispheres, and documented the evolution of the hemispheric growth and the presence of unusual aspects.