en Pediatric Hematology & Oncology Pediatric Hematology & Oncology پژوهشي Original Article Background: Regarding the significance of abdominal masses in children, we aimed to identify the pathology of masses according to the age and sex groups. Materials and Methods: We retrospectively reviewed pathological reports of 461 patients with abdominal mass that underwent resection or biopsy during the study period (25 years). Results: One hundred and eighty six cases (40%) were non-neoplastic, many of which had renal originand 35 cases (7%) were hydatid cysts. Concerning the 271 neoplastic masses (58%), 96 cases (20%) were diagnosed as renal tumors (frequently Wilm’s tumor), 63 (13%) as neuroblastoma and 56 (12%) as abdominal lymphomas. Conclusion: Abdominal masses in children coming to a referral pediatric surgery center are more likely to be neoplastic. We also found that malignancies are rare in neonatal period in comparison to other age groups. Keywords: Abdominal mass, neoplastic, hydatid cyst, wilm’s tumor, neuroblastoma Abdominal mass, neoplastic, hydatid cyst, wilm’s tumor, neuroblastoma 31 34 http://ijbc.ir/browse.php?a_code=A-10-1-13&slc_lang=en&sid=1 H Pourang 10031947532846001127 10031947532846001127 No S Sarmadi 10031947532846001128 10031947532846001128 Yes M Mollaeian 10031947532846001129 10031947532846001129 No S Sanii 10031947532846001130 10031947532846001130 No H Nahvi 10031947532846001131 10031947532846001131 No M Azarshahin 10031947532846001132 10031947532846001132 No MA Ehsani 10031947532846001133 10031947532846001133 No E Shahgholi 10031947532846001134 10031947532846001134 No