Intraoperative electrical stimulation of dorsal spinal roots from L1 to S1 bilaterally was performed in 80 patients affected by cerebral palsy, in whom spasticity was the main symptom. Clinical examination and EMG recordings showed three main features of reflex responses. We know that they indicate respectively a normal presence, a defect or an excess of inhibitory activity within the spinal circuits examined. Only those roots or rootlets involved in circuits where normal inhibitory processes are reduced or absent are surgically sectioned. Therefore these circuits are interrupted. The theoretical bases and long-term results indicate that this method is a useful and correct approach to the neurosurgical therapy of spasticity. It allows us to utilize a new important criterion to identify the roots or rootlets to be sectioned, based not on the anatomic, but on the functional selection.