Dermatomyositis are an heterogen diseases, which are caracterization by information and destruction muscular fibres, taken to diminution muscular force. This are an idiopathic inflammatory myopathies diseases, an autoimun diseases whit an genetic determination. Dermatomyositis affectation the voluntary muscle, skin, and rarely other part of body. It is the most frecvent inflammatory myopathies on childhood. The clinical symptomatology it show an specific heliotrop rush, proximal muscular affectation, the muscular enzime are high, the EMG it show an miogen route, and the muscular biopsy it show perifascicular atrophy.The treatment consist from corticoteraphy in high doses for a long time. It is important to know all the diseases with myositis assotiation to make an corect diferenţial diagnostic.