A case is reported of a 3 year old boy with an acute history of cerebellar impairment and x ray evidence of apparent chest infection. At postmortem examination, his lungs but not the nervous system were found to be massively infiltrated by Langherans histiocytes. In retrospect, the acute ataxia was diagnosed as a paraneoplastic phenomenon secondary to Langherans cell histiocytosis (LCH). This represents a unique occurrence complicating LCH in childhood.