Rasagiline is a monoamine oxidase type-B inhibitor used as monotherapy or in addition to levodopa in the treatment of Parkinson's disease (PD). This naturalistic single-blind study was aimed at evaluating the rapidity of onset effect of rasagiline on motor symptoms in a cohort of early relatively elderly PD patients. 102 outpatients (55 males, median age 71 years) have been selected: 26 were PD therapy-naive and 76 received rasagiline as add-on therapy. The third section of the Unified Parkinson's Disease Rating Scale (UPDRSIII) and the Hoehn-Yahr (HY) scale were assessed at baseline and after 1 and 4 weeks thereafter. The mean UPDRS III total score (-6.7 at week 1 and -8.9 at week 4) and single items, as well as mean HY score (-0.40 at week 1 and -0.67 at week 4), significantly decreased from baseline (p < 0.001). Improvements were significant in both therapy-naive and add-on therapy patients: the mean decreases from baseline to week 4 in UPDRSIII and HY score were -8.8 and -0.46, and -9.0 and -0.74, respectively, in the two subgroups. The mean decrease from baseline in UPDRSIII and HY score did not significantly differ in patients aged > or ≤71 years. Rasagiline had a rapid therapeutic effect from the first week of therapy, which further improved at 4 weeks. The rapid onset of action and the absence of a dose titration are important issues in the management of the PD patient.