We report effects for up to 100 Mrad () gamma-ray exposure on polycrystalline ZnO thin film transistors (TFTs) deposited by two different techniques. The radiation related TFT changes, either with or without electrical bias during irradiation, are primarily a negative shift and a smaller shift ( and for 100 Mrad () exposure). Field-effect mobility remains nearly unchanged. Both, and shifts are nearly completely removed by annealing at for 1 minute and some recovery is seen even at room temperature. We find that our ZnO TFTs are insensitive to electrical bias during irradiation; that is, unbiased measurements are useful worst case test results. To the best of our knowledge, these are the most radiation-hard thin film transistors reported to date.