We describe a 73-year-old forest owner with widespread erythema, myalgia, and proximal muscle weakness. The clinical signs and the results of electromyography, magnetic resonance imaging, and a muscle biopsy were consistent with dermatomyositis. However, serology was positive for Borrelia burgdorferi. More importantly, B burgdorferi DNA was detected in skin by polymerase chain reaction techniques, and spirochete-like organisms were detected in the muscle by silver staining. Lyme disease with muscle involvement can mimic or trigger dermatomyositis and should be considered in the differential diagnosis of dermatomyositis.