Diamond deposition from the fluorinated hydrocarbons CF4 and CHF3 was investigated in a hot filament chemical vapour deposition (HFCVD) system. The systems H-2-CF4, H-2-CHF3 and H-2-CH4 were compared under equivalent conditions. Our results demonstrate that below 650 degrees C the diamond growth rate for H-2-CHF3 gas mixtures is higher than that for the H-2-CH4 system. Even at 400 degrees C it was possible using H-2-CHF3 to measure considerable growth rates with in situ laser interferometry. Mass spectrometry proved the formation-of HF at a significant concentration for the system H-2-CHF3. This is due to the abstraction of F from CHF3 by atomic hydrogen. CFx radical species are postulated from CHEMKIN calculations. They are supposed to play an important role in the diamond growth process using CHF3. With H-2-CF4 mixtures neither diamond nor amorphous graphitic carbon could be deposited. Mass spectrometry showed the inertness of CF4 under the conditions of our investigations with the absence of the F abstraction reaction.