Energy loss spectra for gamma rays incident on sodium‐iodide crystals have been calculated by the Monte Carlo method. The calculations have been carried out for point sources, disk sources, and broad parallel beams of monoenergetic gamma rays varying in energy from 0.279 to 8 Mev. The crystals considered were right circular cylinders varying from small crystals of height and diameter one inch to large crystals of height and diameter 6 inches. Also calculated simultaneously with the energy loss spectra were the efficiencies and total absorption fractions.