There is a paucity of large animal models to study both the extent and the health risk of ionizing radiation exposure in humans. One promising candidate for such a model is the minipig. Here, we evaluate the minipig for its potential in gamma-H2AX-based biodosimetry after exposure to ionizing radiation using both Cs137 and Co60 sources. gamma-H2AX foci were enumerated in blood lymphocytes and normal fibroblasts of human and porcine origin after ex vivo gamma-ray irradiation. DNA double-strand break repair kinetics in minipig blood lymphocytes and fibroblasts, based on the gamma-H2AX assay, were similar to those observed in their human counterparts. To substantiate the similarity observed between the human and minipig we show that minipig fibroblast radiosensitivity was similar to that observed with human fibroblasts. Finally, a strong gamma-H2AX induction was observed in blood lymphocytes following minipig total body irradiation. Significant responses were detected 3 days after 1.8 Gy and 1 week after 3.8 and 5 Gy with residual gamma-H2AX foci proportional to the initial radiation doses. These findings show that the Gottingen minipig provides a useful in vivo model for validation of gamma-H2AX biodosimetry for dose assessment in humans.