Purpose: To characterize the efficacy and safety of palifermin in reducing the incidence of oral mucositis (OM) and diarrhea when administered to patients with metastatic colorectal cancer (CRC) receiving fluorouracil/leucovorin (FU/LV) chemotherapy. Patients and Methods: Patients (N = 64) were randomly assigned to receive either placebo or palifermin (40 μg/kg for 3 consecutive days) before each of two consecutive cycles of chemotherapy with FU/LV. The incidence of OM and diarrhea, safety, disease progression, and survival were evaluated. Results: Thirty-six patients received placebo and 28 patients received palifermin. The incidence of WHO grade 2 or higher OM was lower in patients who received palifermin compared with placebo (29% v 61% in cycle 1; 11% v 47% in cycle 2). FU dose reductions in the second chemotherapy cycle were more frequent in the placebo group (31%) than in the palifermin group (14%). Investigators reported lower mucositis scores and patients reported less severe symptoms with palifermin. There were no statistically significant differences in the incidence or severity of diarrhea or in overall survival between the groups. Overall, palifermin was safe and well tolerated. Conclusion: Palifermin administered at the indicated dosing regimen (40 μg/kg for 3 consecutive days) before chemotherapy was well tolerated and resulted in a statistically significant and clinically meaningful reduction in the incidence of WHO grade 2 or higher OM in patients with metastatic CRC.