A rare case of adult onset Langerhans' cell histiocytosis associated with dysgerminoma in a 35 year old Chinese woman is reported. The patient had a history of dysgerminoma of left ovary 15 years previously and had undergone surgery followed by radiotherapy and an uneventful recovery. She presented again in March 1994, this time with a left clavicular mass, which was shown histologically to be Langerhans' cell histiocytosis. The report illustrates the probable association between the two lesions, with some discussion on the underlying pathogenesis.