The syndrome of megalencephaly, mega corpus callosum and complete lack of motor development (MCC; OMIM 603387) is an apparently rare condition since only three sporadic cases have been reported [Gohlich-Ratmann et al. (1998); Am J Med Genet 79:161–167]. We describe an additional case that was not diagnosed until age 15 months. The MRI showed generalized, severe enlargement of the corpus callosum and thickening of the cortex. The cause for the MCC syndrome is unknown and both autosomal recessive and spontaneous dominant genetic mechanisms are possibilities. © 2007 Wiley-Liss, Inc.