Mutations in the CLCN5 gene, mapped in Xp11.22, have been recently reported to be associated with X-linked nephrolithiasis, X-linked recessive hypophosphataemic rickets and Dent's disease. We report a missense mutation in exon 6 of the CLCN5 gene. The mutation in this pedigree is S244L, the same mutation as has previously been described in an Italian family showing a similar pathology. However, in the family reported here, affected males have developed neither nephrolithiasis nor nephrocalcinosis. The question arises whether we are dealing with a milder phenotype or whether a more severe pathology will develop with ageing.