Objective: To describe the clinical, laboratory, and histopathologic features of idiopathic steatohepatitis in children. Study design: Retrospective review of all liver biopsies performed at Boston Children's Hospital, Massachusetts General Hospital, and the University of Massachusetts Medical Center from 1991 to 1994. Chart review was performed when biopsies demonstrated steatosis. Results: Eighty-two patients had biopsy-proven hepatic steatosis. Fourteen patients had fatty liver without evidence of inherited, infectious, autoimmune, endocrinologic, toxicologic, or iatrogenic causes. All 14 patients were obese, averaging 159% of ideal body weight (range, 121% to 222%). Nine patients initially had transient abdominal pain, two had hepatomegaly, and one was identified by incidental laboratory evaluation. These 12 patients had biopsies because of persistent elevations of aminotransferase levels. Two other patients without risk factors for steatosis were identified at staging laparotomy for Hodgkin lymphoma. The 10 boys and 4 girls had an average age of 13.5 years (range, 10 to 18 years). Aminotransferase elevations were modest, with aspartate aminotransferase and alanine aminotransferase values averaging 77 ± 38 IU and 129 ± 73 IU, respectively. All had imaging studies demonstrating diffuse fatty change. Histologic examination of biopsy specimens revealed varying degrees of steatosis with inflammation and fibrosis. Conclusion: Idiopathic steatohepatitis occurs predominantly or exclusively in obese peripubertal children. This entity represents a frequent reason for liver biopsy in this age group. The degree of steatosis, fibrosis, and inflammation does not correlate with symptoms or signs, and significant liver injury with bridging fibrosis may be present. (J PEDIATR 1995;127:700-4).