A new family with a non-specific X-linked mental retardation (MRX55) is described. An X-linked recessive inheritance is suggested by the segregation from two healthy transmitting females of moderate mental retardation in three males, without any specific clinical, radiological or biological features. Two point linkage analysis demonstrated significant linkage between the disorder and several markers in Xp11 (Zmax = 2.11, theta = 0); multipoint linkage analyses confirmed the significant linkage with a maximum lod score (Z = 2.11 at theta = 0, at DXS8012). Recombination events observed with the flanking markers DXS1068 and DXS1275 delineate a 34 centimorgan interval in the pericentromeric region. The interval of assignment pointed out in this family overlaps with several MRX loci previously reported in Xp11 which are reviewed here in.