Polarimetric radar measurements are corrupted by numerous error sources which limit the ability to derive true scattering coefficient information. The coupling between the polarimetric channels, gain imbalance between channels, and the influence of the system noise floor may all have detrimental impact on the measurement accuracy. These error sources and the relative impact of each of them will differ from radar to radar. Also, the impact of the error sources is dependent on the true scattering properties that are being measured. The importance of each of the error sources is examined by a perturbation study. Then the error effects are quantified by determining the worst-case error as a function of radar parameters and scatterer parameters. These worst-case distortion errors will be discussed along with the practical limits for removing the various sources of error.