We have investigated the structure of 1,2,4,5-tetranitroimidazole (I) by using various levels of theories. We have optimized the geometry of I fully at AM1, PM3, HF/3-21G, HF/6-31G**, HF/6-311 + + G**, MP2/6-31G**, and BP86/6-31G**. A significant difference in optimized geometries is observed depending upon the calculational level, especially by including electron correlation. However, the geometry optimized by the PM3 method may be of practical use to derive molecular properties of nitroimidazole derivatives, including heat of formation and molar volume. All the theories utilized in this study agree that I is stable in the potential energy surface.