Various clinical classifications of XLMR have been reported. In a recent review on X-linked mental retardation (XLMR) genes, 127 conditions featuring XLMR as a primary or major manifestation were listed (32). In our clinical departments, we have a special interest in families of male patients with mental retardation and neurological symptoms. Since the combination of XLMR and neurological manifestations could be found in almost all categories of the previously reported classifications, we outlined a nosological approach meant for those cases where other specific symptoms are lacking.