DNA samples from nine previously reported patients with X-linked recessive glycerol kinase deficiency, associated in seven of them with adrenal hypoplasia and in five with developmental delay and myopathy, have been studied for deletions of the Duchenne/Becker muscular dystrophy gene by probing with the entire cDNA for the dystrophin protein. All five patients with myopathy, including two in whom no deletions had been detected before, were found to have variable-sized deletions extending through the 3' end of this gene. The 5' deletion breakpoints are intragenic in four cases and have been mapped precisely on the exon-containing HindIII fragment map. A correlation was found between severity and progression of the muscular dystrophy phenotype and the sizes of the gene deletions. In cases in which there was glycerol kinase deficiency/adrenal hypoplasia microdeletion syndrome without myopathy, no deletions were found with the dystrophin cDNA.