The structure of two novel 2-(N'-benzylidenehydrazino)-4-trifluoromethyl-pyrimidines has been determined by X-ray crystallography and their energy-minimized structures were stablished by molecular orbital calculations (AM1) by means of comparison. Additionally, the bond lengths of the compounds were analyzed in order to verify the occurance of electronic resonance. Bond lengths and bond angles in the pyrimidine ring and the benzylidene portion compare well with those found in similar compounds. 2-(N'-benzylidenehydrazino)-4-trifluoromethyl-pyrimidine, crystallized in the triclinic space group P-1 solvated with a molecule of water, while 2-(N'-2-methyl-benzylidenehydrazino)-5-methyl-4- trifluoromethyl-pyrimidine crystallized in the tetragonal space group P41. The azomethine moieties showed a trans-planar conformation. The energy-minimized structures of both compounds are in good agreement with their X-ray crystal structures. Nevertheless, a significant difference between calculated and experimental data regarding to the ring planarity was observed due to relevant intermolecular interactions in the real structures. Finally, aromaticities of both pyrimidines and phenyl rings were determined using HOMA calculations.