Introduction: International Study Group of Pancreatic Fistula (ISGPF) grade C postoperative pancreatic fistulas (POPF) are the greatest contributor to major morbidity and mortality following pancreatoduodenectomy (PD); however, their infrequent occurrence has hindered deeper analysis. This study sought to develop a predictive algorithm, which could facilitate effective management of this challenging complication. Methods: Data were accrued from 4301 PDs worldwide. Demographics, postoperative management, and microbiological characteristics of grade C POPFs were evaluated. American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) preoperative and intraoperative variables were compared between grade C POPFs and a 639-case sample of non-grade C POPFs. Risk factors for grade C POPF formation were identified using regression analysis. Results: Grade C POPFs developed in 79 patients (1.8 %). Deaths (90 days) occurred in 2.0 % (N = 88) of the overall series, with 35 % (N = 25) occurring in the presence of a grade C POPF. Reoperations occurred 72.2 % of the time. The rates of single- and multi-system organ failure were 28.2 and 39.7 %, respectively. Mortality rates escalated with pulmonary, renal, and neurologic organ failure, but they were unaffected by reoperation(s). The median number of complications incurred was four (IQR: 2–5), and the median duration of hospital stay was 32 (IQR: 21–54) days. Warning signs for impending grade C POPFs most often presented on postoperative day (POD) 6. Adjuvant chemotherapy might have benefited 55.7 % of grade C POPF patients, yet it was delayed in 25.6 % and never delivered in 67.4 % of these patients. Predictive models for grade C POPF occurrence based on preoperative factors alone and preoperative and intraoperative factors yielded areas under the receiver operating characteristic curve of 0.73 and 0.84 (both P < 0.000001), respectively. Conclusion: This global study represents the largest analysis of grade C POPFs following PD. It describes the severe burden that grade C POPFs incur on patients, with high rates of reoperation and infection, while also potentially worsening overall survival by causing death and delay/omission of adjuvant therapy. Additionally, aggressive clinical management for these POPFs did not improve or worsen 90-day mortality. Predictive tools developed through these data may provide value in managing this difficult complication.