It has been suggested that in patients with Parkinson’s disease (PD) metabolism of the MAO-B inhibitor selegiline to methamphetamine may contribute and/or exacerbate sleep problems, possibly leading to deficits of cognition. This open-label exploratory study included 30 PD patients currently being treated with selegiline (7.5 mg/day) and complaining of sleep disturbances. The aim of the study was to determine whether switching from selegiline to another MAO-B inhibitor without amphetamine-like metabolites, namely rasagiline, would improve sleep behaviour and cognitive function in PD patients. Pathologic aberrations as determined by comparison of the frequency pattern of patients to a database consisting of healthy subjects revealed an approximation of electric brain activity to normality. For verification of efficacy, a combination of questionnaires, quantitative source density EEG recording with CATEEMò and performance of two psychometric tasks (d2-test of attention and reading) during the EEG recording were done on the last day of selegiline treatment (7.5 mg/day) as well as 2 and 4 months later, during which the patients were treated with rasagiline (1 mg/day). In addition, performance of the mental tasks revealed a statistically significant (p < 0.05) increase of theta power (4.75 - 6.75 Hz) indicative of improved cognitive abilities at the end of the treatment period. At the same time evaluation of the psychometric test results indicated a statistical improvement with respect to the score of the d2-test (increase from 6.54 to 7.37; p < 0.05). Serum levels of methamphetamine were measured before and after intake of selegiline or rasagiline. They were correlated to alpha2 power, which is under dopaminergic control, within the temporal lobe. From these results it is concluded that the switch from selegiline to rasagiline not only improved sleep behaviour as reported separately but also had a positive effect on electric brain activity and on cognition in these patients.