Diagnosis of Lyme disease based on dermatologic manifestations. Lyme disease, or Lyme borreliosis, is an infection caused by the spirochete Borrelia burgdorferi, which is most commonly transmitted to humans by a tick bite. Characterized by early and late phases, Lyme disease is a multisystem illness involving the skin, heart, joints, and nervous system. Diagnosis is based predominantly on clinical manifestations, the most specific being dermatologic. Thus, recognizing the dermatologic manifestations of Lyme disease is important for diagnosis and institution of appropriate, effective therapy. Approximately 75% of patients with Lyme disease present with the pathognomonic skin lesion erythema migrans, an expanding erythematous lesion. During early infection, secondary erythema migrans lesions or Borrelia lymphocytoma may occur. Borrelia lymphocytoma commonly presents as an erythematous nodule on the ear lobe or nipple. During late infection, acrodermatitis chronica atrophicans, an erythematous, atrophic plaque unique to Lyme disease may appear; it has been described in about 10% of patients with Lyme disease in Europe. Fibrotic nodules associated with acrodermatitis chronica atrophicans as well as other sclerotic and atrophic lesions, such as morphea, lichen sclerosus et atrophicus, anetoderma, and atrophoderma of Pasini and Pierini, have been seen late in the course of Lyme disease. In a few cases, other sclerodermatous lesions, such as eosinophilic fasciitis and progressive facial hemiatrophy, have been linked to B. burgdorferi infection. We review the cutaneous lesions associated with Lyme disease. 