The aim of this study was to provide a quantitative assessment of pure dystonia in a group of children. Kinematic and muscular characteristics of unconstrained movements of the upper limb, reaching and writing, were investigated. During reaching, the distinguishing factors of dystonic movement were reduced velocity, loss of muscular activation focalization, and impairment of rest-movement modulation. Muscular parameters were able to linearly discriminate the different levels of severity. These results support the hypothesis that basal ganglia dysfunction is responsible for compromising the motor activity focusing. The handwriting movement revealed that the kinematic coordination was altered depending on dystonia severity scores. The 2 protocols revealed themselves feasible and sensitive for detecting even local and subclinical signs. Hence, this work provides a contribution toward a reliable assessment of pure dystonia, crucial for clinical characterization of patients and evaluation of the different treatment options.