Deep brain stimulation of the subthalamic nucleus has been proved to be an effective treatment for advanced Parkinson's disease when therapeutical strategies have failed. A correct selection of candidates for surgery is fundamental to obtain a good clinical effect. In this study we present our protocol of patient selection. In addition we report the data relative to the different causes of exclusion and the clinical efficacy of the electrical stimulation of the subthalamic nucleus at 3 months and 1 year follow-up.