We describe an infant with adrenal insufficiency who was subsequently diagnosed with Duchenne muscular dystrophy (DMD) and hyperglycerolemia due to glycerol kinase deficiency. Karyotyping showed a deletion on the short arm of the X chromosome (p21.1 to p22.1). Molecular mapping revealed that the deletion extended from the 3' end of the DMD gene to a site telomeric to the loci for X-linked congenital adrenal hypoplasia and glycerol kinase deficiency. These results are diagnostic for an Xp21 contiguous gene deletion syndrome--so named because the deletion manifests as a distinctive cluster of otherwise unrelated single-gene disorders in the same individual. The Xp21 syndrome should be considered in any infant with adrenal insufficiency. Measurement of serum triglycerides (without glycerol blanking) and creatine kinase activity are simple screening tests that may facilitate early diagnosis and appropriate genetic counseling about risks of recurrence in subsequent offspring.