Twenty-six Krukenberg tumors (16 lower gastrointestinal, 4 upper gastrointestinal, and 6 of unknown origin) and their primaries when known were stained with CDX2, SATB2, GATA3, TTF1, and PAX8 using a tissue microarray containing predominantly or exclusively signet ring cells. The most common primary was appendiceal mixed adenoneuroendocrine carcinoma. CDX2 and SATB2 were positive in all known lower gastrointestinal primary tumors and negative in nearly all known upper gastrointestinal primary tumors. Primaries showed identical immunophenotypes to their metastases. Among cases of unknown primary origin, 3 were positive and 3 were negative for CDX2 and SATB2. Chest images, upper endoscopies, colonoscopies, appendectomies, and mammogram were performed with negative results in all, 4, 2, 2, and 1 cases, respectively. No cystoscopies were attempted. PAX8, GATA3, and TTF1 were negative in all cases. The literature was reviewed with emphasis on immunohistochemistry of signet ring cell–containing carcinomas from the appendix, colon, stomach, breast, lung, and bladder. Three quarters of gastric primaries stain for CDX2 and only rare examples stain for SATB2. Colorectal primaries (most of them) and appendiceal primaries (all of them) are positive for CDX2 and SATB2. GATA3 stains almost all breast primaries and approximately half of bladder primaries. All pulmonary primaries are positive for TTF1. PAX8 is negative in the gastric, colorectal, and appendiceal primaries reported. This study shows that the panel of immunostains is useful in confirming the site of origin of a metastatic Krukenberg tumor when one is known and has limited diagnostic value for diagnosing metastases of unknown origin.