A stereophotogrammetric technique (ISIS scanning) was used to assess the back shape of children with adolescent idiopathic scoliosis (index cases), their unaffected relatives, normal adults and children, and children with small idiopathic scoliotic curves (Cobb's angle less than 30 degrees) to detect any familial trends that may predispose to scoliosis. The analysis revealed a characteristic three-dimensional scoliotic back shape; no differences in unaffected relatives as regards sex or a positive family history of scoliosis; similar back shapes in unaffected parents and normal adults, both of whom differ from index cases and children with small curves. Unaffected siblings had a sagittal profile between those of normal children and children with small curves. This may represent an inherited tendency to scoliosis.