The thigh muscles of two patients with dermatomyositis (DM) without muscle weakness or conspicuous creatine kinase elevations were studied by magnetic resonance imaging (MRI). Myositis limited to the vastus intermedius muscles (VIM) was detected in both patients, and in one, the diagnosis was confirmed by the findings of a biopsy specimen. Focal myositis of the VIM in early-stage DM, which otherwise would remain hidden by the relatively small muscle size and deep location, can be detected by MRI.