Carcinomas of unknown primary (CUP) are highly malignant diseases which have poor prognosis. We report in the present study the impact on survival and toxicity of a salvage chemotherapy with 5-Fluorouracil (5-FU) and leucovorin (LV) in 25 patients with CUP who failed first-line treatment with cisplatin-based regimens. Chemotherapy was a bimonthly regimen of intravenous LV 200 mg/m2 as a 2-hour infusion followed by a 1-hour bolus 5-FU 400 mg/m2 and a 22-hour continuous infusion 5-FU 600 mg/m2 for 2 consecutive days every 2 weeks. The median number of cycles per patient was 4. Overall toxicity was mild. No objective response was observed. From the start of second-line chemotherapy, the median overall survival was 3 months. The median overall survival from diagnosis was 9 months. Second-line chemotherapy with 5-FU/LV has no impact on survival in patients with CUP.