The goal of this study is to evaluate the effects of robot-assisted upper limb therapy in subacute and chronic stroke patients using a set of kinematic parameters evaluated during each of the first 15 rehabilitation sessions. Twenty-four post-stroke subjects, twelve subacute and twelve chronic, participated in the study. A 2 DOFs robotic system was used for upper limb training. Kinematic parameters related to the speed and smoothness measured at the robot's end-effector were computed. Outcome clinical measures show a decrease in motor impairment at half-treatment both in chronic and subacute patients. Significant improvements in kinematic parameters within the first 15 sessions were observed only in subacute patients.