This study presents the evaluation results of a clinical trial of robotic-assisted rehabilitation in Virtual Reality performed with the PERCRO L-Exos (Light-Exoskeleton) system, which is a 5-DoF force-feedback exoskeleton for the right arm. The device has demonstrated itself suitable for robotic arm rehabilitation therapy when integrated with a Virtual Reality (VR) system. Three different schemes of therapy in VR were tested in the clinical evaluation trial, which was conducted on a group of nine chronic stroke patients at the Santa Chiara Hospital in Pisa-Italy. The results of this clinical trial, both in terms of patients performance improvements in the proposed exercises and in terms of improvements in the standard clinical scales which were used to monitor patients receovery are reported and discussed. The evaluation both pre and post-therapy was carried out with both clinical and quantitative kinesiologic measurements. Statistically significant improvements were found in terms of Fugl-Meyer scores, Ashworth scale, increments of active and passive ranges of motion of the impaired limb, and quantitative indexes, such as task time and error.