Langerhans cell histiocytosis (LCH) is a rare disorder characterized by clonal expansion of antigen presenting Langerhans cells. Different clinical features can be seen according to the involved organs and sytems. Multisystem disease with organ dysfunction is more common in infants, whereas single system disease is usually observed in older children. The disease can affect any system or organ throughout the body. Thymus is a rarely involvement site reported in LCH and usually is accompanied by skin, bone or lung disease. Here we report a 12-year-old male with thymic involvement by LCH clinically mimicking lymphoma. Pediatr Blood Cancer 2008;51:833-835. (C) 2008 Wiley-Liss, Inc.