A process of evaluating robustness of the side slip angle estimation and control algorithms for vehicle dynamics control is described and selected results are presented. The estimation algorithm is a non-linear observer with adaptation to road friction and a compensation for a road bank angle. The estimator relies on the information from the sensors and other estimates, on a nominal model of vehicle, and on assumptions about disturbances, all of which may be inaccurate. In order to evaluate the effects of these errors on the estimation of side slip angle, a systematic robustness study is performed. It uses analysis, vehicle testing and simulations based on a validated vehicle model. First, the effects of single factors in various maneuvers and road conditions are examined and those having the largest contributions to errors are identified. Subsequently, the combinations of multiple error factors are studied, with the emphasis on the worst possible combinations. The robustness of the control system is then evaluated along the same lines, with the particular emphasis on the worst case scenarios, when the side slip angle estimates are the least accurate.