classic congenital adrenal hyperplasia due to 21-hydroxylase deficiency (MONDO_0008728, a Monarch Disease Ontology term) is the most common form of congenital adrenal hyperplasia (CAH), characterized by simple virilizing or salt wasting forms that can manifest with genital ambiguity in females and with adrenal insufficiency (in both sexes), and that presents with dehydration, hypoglycemia in the neonatal period (that can be lethal if untreated), and hyperandrogenia. Also known as: 21-OHD, classic 21-OHD CAH.