Objective: To evaluate the effects of rituximab (anti-CD20 monoclonal antibody) on the disease course in pediatric patients with multisystem autoimmune diseases. Methods: Four patients with multisystem autoimmune diseases refractory to conventional immunosuppressive medications, each with central nervous system (CNS) involvement, were treated with four weekly infusions of rituximab. Their clinical and laboratory responses were evaluated. Results: Each of the patients had improvement in clinical symptoms and laboratory parameters. One patient with autoimmune cytopenias and autoimmune CNS and peripheral nervous system disease had resolution of the cytopenias and marked improvement in neurologic symptoms; he currently receives no immunosuppressive medications. Two half-siblings with lymphoplasmacytic colitis, pulmonary nodules, and CNS disease had improvement of their symptoms. A fourth patient with chorea and seizures secondary to primary antiphospholipid antibody syndrome had improvement in fine and gross motor function and reduced seizure frequency. There were no serious adverse events. Conclusions: The biologic response modifier rituximab, designed to eliminate B lymphocytes, was safe and effective in four pediatric patients with multisystem autoimmune disorders. It appears to be beneficial in autoimmune conditions presumably mediated by a variety of B-cell-related mechanisms, and may decrease or eliminate the need for other immunosuppressive medications.