We have identified a novel DAX1 frameshift mutation (1301delT) at codon 434 in a patient with primary adrenal insufficiency. This 11-day-old boy was admitted to the hospital with hyponatremia, hyperkalemia, and suspected congenital adrenal abnormality. He exhibited severe hypoglycemia, pallor of the skin, buccal and genital hyperpigmentation, hypotension (90/45 mm Hg), anemia, and diarrhea. Although basal gonadotropins were low, and responded minimally to exogenous GnRH, the size of his testes began to increase at age 4 and reached 4.5 mL at the age of 9 years and 8 months. Testosterone levels were prepubertal. These findings further emphasize the variable clinical presentation in children with DAX1 gene mutations and indicate the value of genetic testing in boys with primary adrenal insufficiency.