Fifty families with 101 of their members suffering from idiopathic scoliosis are presented. Twenty-one families were traced to 3rd degree relatives. Historical and clinical examinations were performed in all cases. In 36 patients from 18 families, HLA-A and B loci were measured, and equilibrium function was measured in 93 patients from 20 families. No significant differences were noted between the members of the 50 families studied and a previously studied control group of patients with idiopathic scoliosis with respect to age of the presentation, past history, somatic development, initial curvature and type, and response to treatment. The 21 families in whom 3rd degree relatives were traced did not show any features of a simple Mendelian inheritance. Within 39 families, however, each scoliotic member had the same type of the curve. The study of HLA-A and B loci and equilibrium dysfunction (11 cases in 93 studied, 11.8%) failed to demonstrate a familial pattern. It is concluded that the evidence presented supports the concept of a multifactorial inheritance in 50 families with 101 scoliotic members.