Twenty-one children were diagnosed as having juvenile dermatomyositis on the basis of the strict criteria of Bohan and Peter. In addition to the typical skin and muscle changes, abnormalities of esophageal motility (eight of 19), pulmonary function (14 of 17), ECG (10 of 20), and gastrointestinal absorption of D-xylose (two of eight) with active disease were observed. Clinical signs of other collagen vascular disease appeared in five children. Serologic evaluation demonstrated that ANA and rheumatoid factor were transiently positive in six; one child developed a persistently positive rheumatoid factor after four years of disease inactivity. Antibody to ENA was negative in all, but antibody to PM-1 antigen was present in four of 18. Six had a low C3 or C4; evidence of immune complexes was demonstrated by Clq or Raji binding in eight with active disease. One child was IgA deficient. The HLA-B8 antigen was present in 72% of the Caucasian children as compared with the expected incidence of 21%. Therefore, classical dermatomyositis in children has more systemic involvement then previously appreciated, may be related to the presence of circulating immune complexes, and appears to be under immunogenetic control.