The X- linked Creatine Transporter Deficiency (CTD) is one of three types of the cerebral creatine deficiency disorders. It is caused by mutations in the X-linked gene SLC6A8. We report the first combined 31P and 1H MRS study of CTD patients. Relative concentrations of key metabolites were quantitatively analyzed. The PCr/total-phosphate and total-Cr/NAA ratios were found to be markedly reduced in CTD patients. By combining the proton and 31P data we found that the relative reduction in PCr in CTD patients is much less than that of total Cr.