Teratomas are congenital tumours arising from all three germ cell layers. Retroperitoneal teratoma is very uncommon in the infant age group. Patient commonly presents with progressive abdominal distension and intra-abdominal lump. Teratomas comprises of third most common type of retroperitoneal neoplasm seen in infants and children after Wilms' tumour and neuroblastoma. We hereby report a case of a giant retroperitoneal teratoma in an infant. A 3-month-old female child was admitted with complaint of abdominal distension. Abdominal USG and CT scan revealed a tumour suggestive of retroperitoneal teratoma. Intraoperative finding revealed a large retroperitoneal tumour occupying mainly the whole of the abdomen. Resection of tumour was done successfully.