The psychosocial adjustment of 30 siblings (aged 8–18 years) of children with diabetes mellitus was studied. Although most were younger than the diabetic child, 55% were closely involved in the dietary management and insulin treatment of the diabetes, yet many had only a limited understanding of the disease. Most were well-adjusted. However, low levels of self-esteem were apparent among some subjects, who did not feel free to question their parents about diabetes (30%), who identified themselves as the member of the family most likely to receive blame (33%), and who reported spending more time at home with their families than their peers (40%). Nine children (30%) worried about becoming ill themselves. None believed that having a child with diabetes in the family had impaired relationships in the home. Six siblings (20%) also described some positive effects of the illness, particularly enhanced family closeness.