Primitive neuroectodermal tumors (PNETs) are a type of malignant tumors made up of small neuroectodermal-derived round cells that affect soft tissue and bone, with a wide range of clinical symptoms and histological commonalities depending on the site of the tumor. PNETs account for 4% of all pediatric and adolescent cancers. Here we report a case of a peripheral primitive neuroectodermal tumor in a five-year-old boy. Two days before admission, he complained of multiple attacks of vomiting and one episode of hematemesis, associated with subjective fever, abdominal pain, and distention. He also complained of weight loss and bruises on his face and lower extremities for the last four weeks. Upon physical examination, there was hepatomegaly to the right iliac fossa. Abdominal ultrasound showed that the liver is hugely enlarged with heterogeneous echo texture and smooth borders. A computed tomography scan with contrast showed hepatomegaly to the right iliac fossa region with no focal lesion. Bone marrow aspiration and bone marrow biopsy showed heavy infiltration by monomorphic cells. Moreover, liver biopsy was done for this patient, and it showed metastatic undifferentiated neuroblastoma. Before the liver biopsy results, the patient deteriorated rapidly and dead. Therefore, peripheral primitive neuroectodermal tumors (pPNETs) should be considered in the differential diagnosis of liver masses in young patients to early diagnosis and treatment, and to increase the survival rate.