Adenocarcinoma of the urachus associated with elevated levels of CA 125. Adenocarcinoma of the urachus is a rare genitourinary tumor with a poor prognosis. The treatment of choice is en bloc surgical resection, although combination therapy with surgery and chemotherapy has been used with mixed results. We describe a 69-year-old woman with adenocarcinoma of the urachus and elevated serum levels of CA 125 tumor marker. She was treated with resection plus 5-fluorouracil, doxorubicin and mitomycin, alternating with platinum-based chemotherapy. The serum CA 125 level decreased precipitously after the operation and became normal after 2 months of chemotherapy. The patient remained free of disease 1 year postoperatively. Serum CA 125 may be a useful tumor marker for urachal carcinoma and adjuvant chemotherapy may be effective in treating the disease. 