X-linked intellectual disability-macrocephaly-macroorchidism syndrome is characterized by intellectual deficit affecting both sexes, macrocephaly, and macroorchidism in the majority of affected males. It has been described in 12 individuals from two generations of one family. Other males from this family did not display intellectual deficit but did present macroorchidism and macrocephaly. Transmission is X-linked and the causative gene has been localized to the q12-q21 region of the X chromosome.