Although numerous clinical studies of 'idiopathic' scoliosis have been reported (McCarroll and Costen, 1960; Riddle and Roaf, 1955; Stearns, Jo-Yun Tung Chen, McKinley, and Ponseti, 1955), the aetiology of this condition remains obscure. Such diverse explanations as abnormal vertebral growth, spinal muscle imbalance, postural alterations, and endocrine and metabolic disturbances have found adherents (American Orthopedic Association Research Committee, 1941). The many case reports of specific families having several affected members have implied that hereditary factors might be significant in this disorder (Garland, 1934; Molski, 1957; Sidler, 1938; Staub, 1922), and some investigators have even suggested simple modes of inheritance (Faber, 1936; WynneDavies, 1965). In spite of this previous work, there remains no convincing evidence that idiopathic scoliosis is predominantly influenced by either genetic or environmental factors. This study was undertaken to determine whether idiopathic scoliosis could be demonstrated to follow a predictable mode of inheritance, or to associate with maternal age or birth order.