Background. Liver biopsy is a high-risk procedure in oncology patients, and optimal methods for children have not been established. Objective. To assess the effectiveness and safety of two methods of performing liver biopsy in pediatric oncology patients. Materials ann methods. Between May 1997 and July 1999, 51 liver biopsies (22 percutaneous and 29 transjugular) were performed. The 22 percutaneous biopsies (13 focal hepatic lesions and 9 general liver biopsies) were performed under sonographic guidance; 21 used a spring-loaded needle (usually 18 G). In 21 patients, a coaxial sheath was used to inject a slurry of microfibrillar collagen into the needle track. The 29 transjugular general liver biopsies were performed with a 19-G spring-loaded needle, under sonographic and fluoroscopic guidance. The transjugular technique was used for children with thrombocytopenia, coagulopathy, ascites, or recent bone-marrow transplantation. Results. All biopsies yielded sufficient tissue for diagnostic studies. Bleeding occurred after 3 of 21 percutaneous biopsies, despite coaxial track embolization. No bleeding or other major complication occurred after transjugular biopsy. Conclusion. Coaxial percutaneous biopsy with track embolization was effective, but was not complication-free; it should be reserved for focal lesions or for patients at low risk of bleeding. Transjugular liver biopsy is safe and effective for use in highrisk pediatric oncology patients.