Myositis due to the etiologic agent of Lyme disease, Borrelia burgdorferi, has been reported nine times in the English-language literature; there has been but a single report of exacerbation of dermatomyositis due to B. burgdorferi in a patient with known dermatomyositis. Multiple infectious agents, but not B. burgdorferi, have been hypothesized to trigger dermatomyositis. We report the first case of dermatomyositis that appears to have been triggered by B. burgdorferi. This case involved an individual from Westchester County, NY, who presented with skin lesions suggestive of erythema migrans and who was seropositive for Lyme disease. He soon developed a clinical syndrome suggestive of dermatomyositis: periorbital edema, dysphagia, proximal muscle weakness, and a markedly elevated level of creatine phosphokinase. We also review the clinical presentation and response to treatment of patients with Lyme myositis.