Rasagiline is a MAO-B inhibitor that is currently registered for the symptomatic treatment of Parkinson disease. The ADAGIO trial studied the potential disease-modifying properties of rasagiline in 1100 patients with Parkinson disease, using an innovative 'delayed start' design. Patients were randomized to either immediate treatment or delayed treatment (after 9 months). Two doses of rasagiline were studied: 1 or 2 mg. Both doses relieved the symptoms. However, the group that immediately started on 1 mg showed an extra improvement at the end of follow-up. This could not be explained by the effect on the symptoms, but was possibly a disease-modifying effect. Surprisingly, the 2 mg group did not show this additional effect at the end of follow-up. Therefore no definite conclusions can be drawn with respect to the potential disease-modifying properties of rasagiline. Rasagiline should be prescribed only with the aim of symptomatic relief, but not to curb the progression of Parkinson disease.