Retroperitoneal fibrosis is an unusual cause of obstructive uropathy in the pediatric population. The etiology is unknown although there are laboratory and clinical associations with various autoimmune diseases. Familial associations have not been reported in children. A family is reported where two siblings have idiopathic retroperitoneal fibrosis. In addition, these sisters and the father manifest clinical laboratory evidence for systemic immunologic diseases. These young girls represent the first patients to illustrate both autoimmune and familial characteristics of this disease. These cases support the concept that retroperitoneal fibrosis is a local manifestation of a systemic immune disease.