PURPOSE: As increased level of prostaglandin has been identified in the bony lesions of Langerhans cell histiocytosis (LCH), we speculated that indomethacin, a potent prostaglandin inhibitor, may be effective for patients with LCH. METHODS: Retrospective review of 8 children with LCH (male 7, female 1) treated with indomethacin at Seoul National University Children's Hospital from September 1999 to February 2001 was done. The dose of indomethacin ranged from 1.8 to 2.8 mg/kg/day in two divided doses. RESULTS: Four patients with single bony lesion had a complete response to treatment. Among them one patient was treated with indomethacin after fourth relapse. Two patients with multiple bony lesions seemed to have partial response to treatment with indomethacin initially but showed disease progression later. Two patients with extraosseous lesion did not respond, but skull lesions were resolved after treatment. No serious toxicities of indomethacin treatment were observed. CONCLUSION: Indomethacin seems to be a very convenient and useful therapy for LCH involving single bony lesion. The mechanism how the LCH imporves in response to indomethacin has to be elucidated. Whether it has a specific role in slowing disease progression or we are seeing merely a spontaneous remission has to be studied in large scale.