In order to describe the neurological abnormalities and to identify the gene localisation, we re-evaluated a previously reported family with X linked mental retardation (XLMR). Reliable data were obtained for six of the seven affected males, of whom two had had infantile spasms. Profound MR (IQ<20) was found in one and mild MR (IQ 50-70) in five males. No dysmorphic features, except for macrocephaly in one male, were found. Neurological abnormalities included varying degrees of spinocerebellar involvement. Neuroimaging studies showed abnormalities, such as cerebellar atrophy or corpus callosum hypoplasia or both, in three of the six males. Several affected and unaffected subjects suffered from hyperhidrosis, which appeared to segregate independently as an autosomal dominant trait. Genetic linkage analysis localised the XLMR disease gene to Xp11.4-Xp22.11 with a maximum multipoint lod score of 3.57, overlapping the candidate region recently found in two Belgian XLMR-infantile spasm families. Compared to the Belgian patients, the majority of the affected males in this report had a considerably milder phenotype.