3-Chloro-4-fluoro-1,2,5-thiadiazole has been synthesized and investigated in the gas phase by IR spectroscopy and UV photoelectron spectroscopy. The ground-state geometry of the neutral molecule has been obtained from quantum-chemical calculations using the B3LYP/aug-cc-pV(T+d)Z method. Ionization potentials have been determined and the electronic structure has been discussed within the frame of molecular orbital theory. IR and photoelectron spectroscopies, supported by quantum-chemical calculations at the B3LYP and SAC-CI/aug-cc-pV(T+d)Z levels, provide a detailed investigation into the vibrational and electronic character of the molecule.