AbstractThis paper reports observations following on a study of anorexia nervosa in 34 twins and one set of triplets, and within which approximately half the monozygotic (MZ) twins displayed concordance, compared with 7% of the dizygotic (DZ) twins. One additional case, involving childhood adoptions, is described, wherein neither genetic nor specifically assortative selection factors seem to have been at work. The findings suggest that genetic and environmental factors can interact to contribute to the development of this apparently culture‐based and multifactorially derived condition. A number of possible genetic strands to the condition are proposed; probably not all of them are specifically necessary for its development. The same may apply to experiential influences. Elsewhere it has been argued that the one essential charactistic of anorexia nervosa is avoidance behavior and the factors permitting and facilitating it (Crisp, 1980). Experiential influences, in the form of psychological maturational challenges in adolescence impinging on constitutional propensities to the point of precipitating the disorder out, would seem often themselves to have been influenced by constitutional psychological characteristics and earlier childhood experiences. A further pooling and study of all known twin and adoptive cases might now advance our knowledge of this condition furthe