Endocervical-type mucinous adenocarcinoma (ECA) of the uterine cervix is defined as a tumor composed of cells resembling those of the endocervical glands, but recent studies have demonstrated that a minority of ECAs displays a gastric immunophenotype. The aim of this study was to assess the significance of the gastric phenotype. Fifty-three cases of mucinous adenocarcinoma of the uterine cervix (37 FIGO stage IB, 4 stage IIA, and 12 stage IIB) were reviewed and reevaluated using a newly established morphologic criteria for distinguishing gastric type adenocarcinoma, which was defined as a tumor showing clear and/or pale eosinophilic and voluminous cytoplasm, with distinct cell borders. The results were correlated with gastric immunophenotype, determined by HIK1083 and MUC6 immunostaining, and patient outcome. Following the current World Health Organization scheme (2003), 47 tumors (89%) were classified as ECA, 1 (2%) as intestinal type, 1 (2%) as mixed endocervical and intestinal type, and 4 (8%) as minimal deviation adenocarcinoma. Twelve of 47 (26%) ECAs and all 4 minimal deviation adenocarcinomas, reclassified as gastric type using the novel criteria, were frequently positive for HIK1083 with a rate of 75% (12/16), whereas only 11% (4/37) of nongastric tumors were positive. There was no significant difference in MUC6 reactivity between gastric and nongastric type tumors (31%, 5/16 vs. 16%, 6/37; P=0.4). Patients with gastric-type adenocarcinomas had a significantly decreased 5-year disease-specific survival rate (30 vs. 77%; P<0.0001), and the gastric type morphology was related to a significant risk for disease recurrence compared with the nongastric type (P=0.001; HR, 4.5; 95% confidence interval, 1.42-14.2). HIK1083-positivity was also related to decreased 5-year disease-specific survival rate (38% vs. 74%; P<0.005). Mucinous adenocarcinoma of the uterine cervix with gastric immunophenotype can be a distinct morphologic variant showing an aggressive clinical course.