Mutation in the orphan nuclear receptor DAX-1 gene causes X-linked adrenal hypoplasia congenita (AHC). Affected male children classically suffer a salt-losing crisis and adrenal insufficiency in their early infancy or, in some rare exceptions, with late-onset subtype. We report here a patient manifesting late-onset adrenal hypoplasia congenita caused by the premature truncation of the C-terminus of the DAX-1 molecule, which is essential for its function as a transcriptional repressor. A 12-year-old boy was referred to us after being afflicted with generalized skin pigmentation for about 3 years, fatigue and headache. Primary adrenal insufficiency was determined on the basis of a low plasma cortisol level (3.9 microg/dl) despite an extremely high ACTH level (1200 pg/ml). Replacement therapy with hydrocortisone and fludorocortisone acetate was initiated soon thereafter. Hypogonadotropic hypogonadism was confirmed at the age of 18 years, at which time sexual infantilism had become apparent. Direct sequencing of the peripheral lymphocyte-derived DNA revealed a novel 1033del13 mutation on the ligand-binding domain of the NR0B1 (DAX-1) gene, which generated a premature stop codon truncating the C-terminus. This mutation was considered de novo since we could not find it in his mother. This case demonstrates that even a truncated protein lacking the major functional domain of DAX-1 can present late-onset and latent adrenal failure.