BACKGROUND: Cognitive impairments are common in patients with Parkinson's disease (PD). However little is known about the cognitive effects of dopaminergic therapy. METHODS: The study was a single-blind prospective study of 21 patients with PD. Each patient had received either levodopa (Sinemet(R), n=8) or dopamine agonist (Requip(R), n=13) during 24 consecutive weeks. Neuropsychological battery, including Korean version of Alzheimer's Disease Assessment Scale(R) cognitive subscale (ADAS-Cog) and frontal-executive function part of SNSB (Seoul Neuropsychological Screening Battery), were performed two times, before and after the 24 weeks of management. Patients also received quantitative ratings of motor symptom severity and functional status using Unified Parkinson's Disease Rating Scale (UPDRS) before and after the dopaminergic therapy. RESULTS: After six months of treatment, motor scale improved in both groups (p<0.05) without difference between the groups (p>0.05). In ADAS-Cog testing, Requip(R) group improved at more categories than Sinemet(R) group but without statistical difference (p>0.05). The results of frontal-executive function test did not differ between the groups, either. CONCLUSIONS: Our study does not provide an evidence that dopaminergic treatment improves cognitive functions in Parkinson's disease. Furthermore, we found no significant difference in the effect on cognition between the two tested drugs and no difference in the results of the above-listed neuropsychological tests between the first and the last visits.