Serous papillary carcinomas (SPCs) share a similar morphology regardless of whether they originate from the ovary or the uterus. Identification of the site of origin of the tumor can be a challenging and a diagnostic dilemma, particularly, in the setting of a pelvic mass or peritoneal carcinomatosis. Recognition of the site of origin influences the staging, management, and prognosis of these malignancies. The purpose of this study is to identify a panel of markers to distinguish the ovarian serous papillary carcinomas (OSPC) from the uterine serous papillary carcinomas (USPC). Formalin-fixed, paraffin-embedded archival tissue from 46 cases of SPCs (33 uterine and 13 ovarian) were stained using antibodies for estrogen receptor (ER), WT1, insulin-like growth factor-II mRNA-binding protein 3 (IMP3), p53, and p16. The OSPC expressed ER (92%), WT1 (100%), IMP3 (92%), p53 (92%), and p16 (92%). The USPCs expressed ER (30%), WT1 (64%), IMP3 (85%), p53 (64%), and p16 (76%). Only ER expression was significantly higher in OSPC compared with USPCs (P<0.001). The combined ER+WT1+ phenotype was present in 92% of the OSPC, whereas only 18% of the USPCs had the same phenotype (P<0.001). Furthermore, 71% of the OSPCs expressed ER+, p53+, WT1+, IMP3+, and p16+ immunophenotype, whereas in USPCs, the tumor cells showed immunophenotypic diversity, with only 6% of the USPCs expressing reactivity to all the 5 markers (P<0.001). This study suggests that ER alone or in combination with a limited panel of markers may be used to identify the site of origin of SPCs.