Adrenal hypoplasia congenita (AHC) is a rare inherited disorder of the adrenal cortex commonly manifested as an early onset adrenal insufficiency syndrome. A novel DAX1 (NR0B1) gene mutation was detected in a Turkish newborn boy presenting with primary adrenal insufficiency. He was from a family with a history of unexplained death of three male siblings in the neonatal period. This report highlights the value of mutational analysis of the DAX1 gene for definitive diagnosis of AHC as well as for genetic counselling because this disorder shows an X-linked genetic pattern of transmission, providing the possibility of finding new cases even in presymptomatic individuals.