Although FOLFIRINOX (5-fluorouracil, leucovorin, irinotecan, and oxaliplatin) has been proven efficacious in metastatic pancreatic cancer (MPC), physicians hesitate to administer it due to its hematologic toxicities. We investigated the usefulness of primary granulocyte colony-stimulating factor (G-CSF) prophylaxis. We reviewed electronic medical records of MPC patients with good performance status who were administered FOLFIRINOX as the first-line treatment from 2011 to 2017. The patients were divided into primary G-CSF prophylaxis users (group A) and non-users or therapeutic/secondary users (group B). Cumulative relative dose (cRDI), adverse effects (AEs), and overall survival (OS) were compared. A total of 165 patients (group A (57) vs. group B (108)) were investigated. Intergroup differences in baseline characteristics were not significant, although the cRDI and the number of treatment cycles were both higher in group A than in group B (cRDI: 80.6% vs. 73.9%, p = 0.007; 9 vs. 6 cycles, p = 0.004). Primary G-CSF prophylaxis reduced the risk of neutropenia (55.6% to 31.6%, p = 0.003) and febrile neutropenia (18.5% to 1.8%, p = 0.002) and improved OS (8.8 to 14.7 months; hazard ratio [HR]: 1.766, 95% CI: 1.257-2.481, p = 0.001). When administering FOLFIRINOX for MPC, primary G-CSF prophylaxis could be rationalized to reduced AEs and improve survival; more prospective studies are needed.