Pancreatic and biliary tract carcinomas are very chemoresistant. After a first-line treatment with a gemcitabine-based regimen, no second-line scheme is consolidated in clinical practice. The aim of this study was to evaluate the toxicity and the activity of the FOLFIRI regimen as first-line or second-line chemotherapy in patients with pancreatic or biliary tract tumors. Fifty-four patients (30 with pancreatic tumor, nine with gallbladder tumor, and 15 with biliary tract tumor) were treated with FOLFIRI (irinotecan 180 mg/m2, day 1; leucovorin 100 mg/m2 intravenously, days 1 and 2; 5-fluorouracil 400 mg/m2 intravenous bolus, days 1 and 2; and 600 mg/m2 in 22 h intravenously, continuous infusion days 1 and 2; every 14 days). Toxicity was recorded at each cycle according to the NCI-CTC V3.0 criteria, the response rate was verified each four cycles according to the RECIST criteria, and the progression-free survival rates as well as the overall survival rates were calculated according to the Kaplan–Meier method. Overall, the toxicity was mild. Grade 3–4 neutropenia occurred in 42.6% of patients. Grade 3–4 gastrointestinal toxicity was rare. FOLFIRI as a first-line treatment produced a response rate of 25%. In the second-line group, 9/21 patients (42.9%) obtained a stable disease as best response. In the entire population, the median progression-free survival rates were 3.1 months [95% confidence interval (CI), 1.9–4.4] and 3.5 months (95% CI, 2.6–4.4), respectively, in the first-line and the second-line cohort of patients. The median overall survival rates were 14.5 months (95% CI, 7.0–22.1) and 6.2 months (95% CI, 5.4–7.0), respectively, in the first-line and the second-line cohort of patients. FOLFIRI is feasible and well tolerated in patients with pancreatic or biliary tract tumors; it has a good activity in first line and mostly in patients with pancreatic cancer.