The heights and symptoms of 52 patients, aged at least 18 years, with X-linked hypophosphataemic rickets were analysed retrospectively; 47 had been seen as children and 5 were adult at their first examination. 2 patients were lost to follow-up. 3 patients had died but their adult heights were known. There was no evidence that any form of treatment (ie, vitamin D in high doses, vitamin D plus phosphate supplements, or calcitriol plus phosphate) had any effect on adult height, symptoms, or alkaline phosphatase levels. There was a negative relation between adult height and the number of osteotomies undergone. The complications of treatment, such as renal failure, which occurred secondary to vitamin D intoxication in 3 patients in their twenties, may outweigh any possible benefits. Until a treatment is established as effective in controlled trials, it may be better that these patients remain untreated.