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An 8 year old boy had been bitten by a tick in his left axilla five months ago. A few weeks later, two erythematous macules, each 7–10 cm in diameter, had developed over his left chest and within a month both lesions disappeared untreated. Two months later a red-purple, firm, indolent swelling of his left nipple appeared and increased in size over the next eight weeks (see fig). He was sent to us for biopsy to rule out a tumour. Based on history we made a clinical diagnosis of Borrelia lymphocytoma, refrained from biopsy, and recommended treatment with doxycycline for four weeks. Serological assays (EIA and immunoblot) revealed specific IgG antibodies against Borrelia burgdorferi. One month later the swelling of the nipple had substantially decreased. Another four weeks later the appearance of the boy's nipple was normal. Swelling of a nipple should prompt diagnostic tests for Borrelia burgdorferi infection.