Seven girls and 3 boys with MCTD have been described. As a group their clinical characteristics and serological findings are similar to those reported in adults, with several important differences. Children with MCTD may have marked thrombocytopenia and more frequently they have RF. Significant cardiac and renal involvement are more common in children, may lead to longer and higher dose corticosteroid therapy, and may contribute to a less optimistic prognosis than that described in adults.