Published experience remains limited for glandular neoplasms of the urachus, especially mucinous cystic tumors. We reviewed 55 glandular urachal neoplasms to evaluate their clinical features and histopathologic spectrum and to devise a classification system for the mucinous cystic forms. Within the 55 cases studied, we observed 2 groups with differing clinical, gross, and histopathologic features. The first group, invasive, noncystic adenocarcinomas (n=24), had clinicopathologic features in accord with the known spectrum of urachal adenocarcinoma (mean age 50 y, female:male ratio 1.7, with recurrence or death from disease in 9/16 cases over a 45 mo mean follow-up). The second group, mucinous cystic tumors (n=31), morphologically resembled mucinous cystic tumors of the ovary and appeared classifiable by the same approach (mean age 47 y, female:male ratio 1.4) and included mucinous cystadenoma (n=4), mucinous cystic tumor of low malignant potential (n=22, including 2 cases with intraepithelial carcinoma), and mucinous cystadenocarcinoma with microscopic (n=4) or frank invasion (n=1). Follow-up information was available for 13 patients with mucinous cystic tumors (mean 41 mo); we observed no local recurrence or distant metastasis. This experience suggests that there is a distinct group of glandular, cystic tumors of the urachus that is classifiable in a manner similar to ovarian neoplasms and that has a favorable prognosis after complete excision. As with cystic neoplasms of other organs, rigorous sampling is recommended to identify potentially small foci of carcinoma that could be missed by inadequate sampling. Accordingly, classification based on methods other than complete surgical excision may be hazardous.