This article summarizes current understanding of the pathophysiology of anorexia nervosa. Evidence is reviewed of alterations in hypothalamic‐pitui‐tary‐thyroid mechanisms, catecholamine metabolism, and endogenous opioid activity. It is concluded that once weight loss and starvation occur, the usual mechanisms for release and inhibition of various regulators of eating behavior change, and a new set of regulating mechanisms is instituted. Thus, despite an increased body of knowledge, understanding of the origins of anorexia nervosa still eludes us.