An eleven-year-old boy was diagnosed to have Addison's disease with an ACTH level of over 4500 pg/ml after a short episode of fever and dehydration. From the age of 6 years his skin and buccal mucosa had been hyperpigmented but there were no other subjective complaints. The clinical examination also revealed signs of advanced puberty for his age (3rd--4th stage according to Tanner's criteria), with advanced bone age (13 years). The elevated levels of plasma testosterone and gonadotropins and their response to LH-RH stimulation were appropriate for his clinical stage of puberty and supported the diagnosis of true precocious puberty. It is proposed that the concomitant appearance of Addison's disease and precocious puberty is due to a "drift" phenomenon of LH-RH and/or gonadotropins following the prolonged elevation of ACTH secretion.