We describe a two generation family in which two males have the X linked recessive MASA syndrome (mental retardation, aphasia, shuffling gait, and adducted thumbs). A third male in this family died at the age of 15 years from congenital hydrocephalus. In the present family cerebral abnormalities are reported for the first time. Linkage analysis confirms the chromosome localisation at Xq28. A crossover between the coagulation factor VIII locus (F8C) and MASA syndrome, but not with DXS52 and DXS305, locates the gene on the same side of F8C as DXS52 and DXS305. The possible relationship between MASA syndrome and X linked hydrocephalus is discussed.