Primary lymphedema, a disorder causing persistent swelling in an extremity, is rare in children and adolescents; it affects 1.15/100,000 persons less than age 20 years. It primarily affects girls near menarche. The records of 125 children and adolescents, aged 0 to 20 years, who were examined at the Mayo Clinic were analyzed; 99 of these patients were contacted to obtain follow-up data. The influences of estrogen and inflammation are thought to be important etiologic factors in primary lymphedema. The diagnosis can be made on the basis of a thorough history and physical examination. Lymphangiograms, venograms, and biopsies add nothing to the diagnosis because of the low incidence of tumor in children and adolescents. Conservative treatment is recommended: a Jobst-type stocking, elevation, and proper foot care. Diuretics are not recommended. Careful psychologic counseling, especially in adolescents, is highly recommended.