Assessment of motor disorders forms an important ingredient of neurology, rehabilitation medicine and orthopaedics. Until now, however, many of the employed assessment tools are derived from empirical knowledge. Almost no relation exists with modern theoretical notions about motor control. In the present article, motor control theory is reviewed in the light of its potential contribution to understanding motor recovery. An attempt is made to present a theoretical framework for the assessment of motor disorders related to recent insights in motor control. The framework emphasizes the dynamical character of recovery. The principle of output optimization is discussed and it is stressed that compensation plays a permanent role in adapting to damage of the body or to changes in the environment. An assessment procedure is introduced to measure the (mental) costs of this compensation. It is argued that changes in the costs of compensation across time reflect recovery.