A case of polypoid endocervical adenomyoma (PEA) in the uterine cervix was encountered in the uterine cervix of a 56-year-old woman. Grossly, a well-circumscribed polypoid tumor was observed protruding from the uterine cervix. Based on the findings of imaging studies, it was assumed to be an adenoma malignum in the uterine cervix. The tumor was composed of a mixture of proliferating glands of endocervical type and fascicles of smooth muscle. No distinct nuclear anaplasia, architectural abnormality or any evidence of destructive stromal invasion was observed. Adenoma malignum, which shows a gastric phenotype with immunoreactivity for HIK-1083, was a serious diagnostic possibility. In the present case, the tumor was a well-circumscribed polypoid lesion, with no cytologic or architectural abnormality; however, focal immunoreactivity was shown for HIK-1083, which thus suggested it to be PEA. Therefore, the results of these ancillary diagnostic modalities should be interpreted with caution and combined with the gross and light microscopy findings.