The prevalence of psychotic complications of levodopa treatment was assessed in 198 Parkinson patients. The symptoms were seen in 44 (22.2%). Those who developed complications were significantly older at disease onset (63.3 +/- 9.2 vs 57.6 +/- 11.6). The observed psychiatric symptoms were classified into two categories: simple, including incidents of confusion alone or hallucinations with preserved insight, and complex, including delusions or chronic confusion without preserved insight. Patients with complex symptoms were significantly younger at the onset of the disease, and the duration of the disease prior to these psychiatric symptoms was longer than in the group of patients with simple symptomatology. Patients with complex symptoms were more susceptible to another central side-effect of the treatment: dyskinesias, than those with simple.