Purpose FOLFIRINOX is the standard therapy in patients with unresectable pancreatic cancer (PC). However, FOLFIRINOX frequently induces febrile neutropenia (FN) and neutropenia. The purpose of this study was to explore risk factors for FN and grade 4 neutropenia (NP G4) in patients receiving FOLFIRINOX for PC. Methods We collected data on 106 patients with PC treated with first-line FOLFIRINOX between 2015 and 2017 using the Pancreatic Cancer Cohort Registry of Severance Hospital in Seoul, Korea. Results Multivariate logistic regression analysis showed that female (OR, 3.24; P = 0.023), Eastern Cooperative Oncology Group performance status (OR, 3.70; P = 0.024), overweight (OR, 4.25; P = 0.022), and initial biliary stent insertion (OR, 4.22; P = 0.008) were significantly related to a high risk of FN. Time-dependent bias was reduced using Cox regression analysis, which revealed that female (OR, 2.29; P = 0.041), overweight (OR, 2.67; P = 0.022), and initial biliary stent insertion (OR, 2.59; P = 0.016) were statistically significant predictors. Regarding NP G4, female sex (OR, 2.90; P = 0.016) and overweight (OR, 4.07; P = 0.033) were identified as risk factors in multivariate analysis; however, in Cox regression analysis, tumor in the head of the pancreas (OR, 1.96; P = 0.027) and hemoglobin (g/dL < 12) (OR, 1.87; P = 0.049) were also identified as risk factors. Conclusion Female sex, overweight, and initial biliary stent insertion were independent risk factors for the occurrence of FN in patients with unresectable PC treated with FOLFIRINOX.