Résumé : The free energies of activation for hindered rotation around the C-N bond were determined for a series of N,N-disubstituted thioamides by means of 13C and 1H dynamic nmr. A comparison between barriers for 20 amides and the corresponding thioamides, studied under similar conditions, was drawn up using both our results and data obtained from the literature. An excellent linear correlation was obtained. The same correlation also holds for primary (thio)amides and seems to be of general significance. Subsituent effects on the barrier heights of thioamides and amides are discussed in connection with some particular cases.