Amyotrophic lateral sclerosis (ALS) is a progressive degeneration of the peripheral and central motor neurons. The principal consequence is a loss of motor functions. Evaluation of motor deficit implies an assessment of the resulting deficiency or incapacity and final disability. Many evaluation are proposed for patient follow-up in order to analyze the state of motor function and their consequences on activities of everyday life. Few recommendations can be formulated. Scales must be validated and relatively simple to use and generate ordinate results allowing statistical analysis. The choice of which scale to use depends on the clinical objective. Global scales (ALS Functional rating Scale, ALS Severity Scale, Appel scale, Norris scale and Honda scale) can be used to evaluate progression of the disability. Some of these scales are strongly correlated with patient survival. Other scales (ALS Health State Scale, global clinical impression) are used to classify patients by homogeneous stage of gravity. Still other scales, such as the Sadoul and Borg scales and the Epworth score are designed for more specific evaluation of a given function. The clinician should be aware of these different scales and their relative utility. Knowledge of these scales, their validity, their sensitivity to modification, and their specificity and interpretation pitfalls is a prerequisite to good evaluation in daily practice and clinical research.