A family is described with X-linked mental retardation (XLMR) with affected males in 2 generations. The manifestations are macrocephaly and heterozygous expression. Linkage analysis gives a 2-point lod score of 3.31 (theta = 0.0) at the AR, DXS991, and MAOB marker loci. The gene is localized by recombination events between DXS1068 (Xp) and DXS1125 (Xq). This condition in this family may be similar to that described by Atkin et al., 1985 (Am J Med Genet 21:697-705).