We are reporting our clinical experience in 66 patients with advanced Parkinson's disease (PD) who were switched to tolcapone because of persisting off periods despite treatment with entacapone (according to the European Agency for the Evaluation of Medicinal products: EMEA). We used UPDRS II-III-IV in "on" state to monitor tolcapone effectiveness at 6 and 12 months. We found significant reductions in mean off-time duration (UPDRS item 39) and levodopa dose at follow up. Eleven patients dropped out (17%) during the first month of treatment, 2 (3%) because liver enzymes exceeded normal limit. Amongst patients who continued tolcapone, 30/55 (54%) reported "off-time" reduction > or =25% (UPDRS-39 decrement > or =1 point). Our findings indicate that tolcapone widens the levodopa therapeutic window, even in patients who have not benefited from entacapone. We suggest that tolcapone is indicated before patients are referred for more invasive procedures.