BACKGROUND: Mitochondrial DNA (mtDNA) copy number in peripheral blood has been found to be associated with risk of developing several cancers. However, data on pancreatic ductal adenocarcinoma (PDAC) are very limited. METHODS: To further our knowledge on this topic we measured relative mtDNA copy number by a quantitative real-time PCR assay in peripheral leukocyte samples of 476 PDAC cases and 357 controls nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. RESULTS: We observed lower mtDNA copy number with advancing age (p=6.54×10-5) and with a high BMI level (p=0.004) and no association with sex, smoking behavior and alcohol consumption. We found an association between increased mtDNA copy number and decreased risk of developing PDAC with an OR=0.35 (95% C.I 0.16-0.79), p=0.01 when comparing the 5th quintile with the 1st using an unconditional logistic regression and OR=0.19 (95% C.I 0.07-0.52), p=0.001 with a conditional analysis. Analyses stratified by BMI showed an association between high mtDNA copy number and decreased risk in the stratum of normal weight, consistent with the main analyses. CONCLUSIONS: Our results, suggest a protective effect of a higher number of mitochondria, measured in peripheral blood leukocytes, on PDAC risk. IMPACT: Our findings highlight the importance of understanding the mitochondrial biology in pancreatic cancer.