We present a method of assessing the quality of protein structures based on the use of side-chain NMR chemical shifts. Because these parameters are very accurate reporters of side-chain positions and are highly sensitive to tertiary structure and packing, they are particularly useful for structure validation. To analyze a given structure, we define a quality score, QCS, that compares the chemical shifts calculated from such a structure with the corresponding experimental values in a way that takes account of the errors in the calculations. The results that we report illustrate the advantages in the examination of the quality of protein structures from the perspective of side-chains.