Primary and secondary mucinous tumors can involve the ovaries and have similar histologic appearances. The differential diagnosis is important for surgical and chemotherapeutic treatment and for the prognosis, but often it is extremely difficult. This article discusses an immunohistochemical panel that includes carcinoembryonic antigen (CEA), cytokeratin (CK) 7, CK20, CA125, CA19.9, and a new marker, CDX-2, for the distinction between primary ovarian mucinous carcinomas and metastatic (intestinal) ovarian tumors. Forty-three cases representing primary and secondary ovarian tumors were considered and consisted of 14 primary mucinous ovarian carcinomas (PMOCs) and 29 secondary (intestinal) ovarian tumors (SIOTs). Fisher exact test was performed to evaluate the reliability of the respective antibodies to discriminate between PMOCs and SIOTs. CDX-2 was diffusely positive in all SIOTs and was expressed focally in 3 cases (21.42%) of PMOCs. CK7 was diffusely positive in 13 cases (44.82%) of SIOTs and in 13 cases (92.85%) of PMOCs. CK20 was diffusely positive in 17 cases (58.62%) of SIOTs and in 6 cases (42.85%) of PMOCs. CEA was diffusely positive in 28 cases (96.55%) of SlOTs and in 12 cases (85.71%) of PMOCs. CA 19.9 was positive in all SIOTs and in 12 cases (85.71%) of PMOCs. CA125 was positive in 3 cases (10.34%) of SIOTs and in 4 cases (28.57%) of PMOCs. CK7 and especially CDX-2, a specific and sensitive marker, can aid pathologists in making a differential diagnosis (P = 0.003 and P < 0.0005, respectively), whereas CEA, CK20, CA125, and CA 19.9 markers are not high enough to distinguish between primary and secondary mucinous ovarian tumors.