After a diagnosis of endocervical adenocarcinoma was made on examination of a curettage specimen, a 46-year-old woman underwent laparotomy for the purpose of radical hysterectomy. After frozen section of a biopsy specimen obtained from a nodule 2 cm in diameter on the posterior surface of the cervix was interpreted as adenocarcinoma, consistent with pseudomyxoma peritonei, the planned hysterectomy was abandoned; only biopsies of the pelvic and para-aortic lymph nodes and a bilateral salpingo-oophorectomy were performed. Permanent sections of the nodule revealed pools of almost acellular mucin, myxoid fibrous tissue, and typical endometriotic glands and stroma. Similar findings were associated with endometriotic foci in the serosa of a fallopian tube and adjacent to a pelvic lymph node. There was no evidence of adenocarcinoma in any of the specimens. A radical hysterectomy was performed subsequently, and pathological examination of the uterus revealed a superficially invasive adenocarcinoma of the cervix without evidence of extrauterine spread. The diagnosis of endometriosis associated with myxoid change was confirmed in residual cul-de-sac tissue. The patient was alive with no clinical evidence of tumor 6.5 years later. This case illustrates that rare cases of endometriosis can be associated with striking degrees of myxoid change, a finding that should not be confused with mucinous adenocarcinoma on microscopic examination.