The phenotypic nonspecificity of many forms of X-linked mental retardation has hampered attempts to classify them into clinically homogeneous groups. One such condition, described by Clark and Baraitser [1987: Am J Med Genet 26:13-15], has been the subject of a single pedigree report to date. We now describe a further pedigree whose affected members share many manifestations with those reported by Clark and Baraitser, and we consider the possible distinction between this condition and Atkin-Flaitz syndrome.