Parkinson's disease (PD) has a major socioeconomic impact on society. The chronic, progressive course of the disease, which often leads to severe disability, results in high expenses for the medical resources used for treatment, care, and rehabilitation of patients as well as reduced or lost productivity as a result of illness or premature death. In Great Britain, it has been estimated that the National Health Service spends up to 383 million pound sterling (1992) annually for the care of PD. This emphasizes the importance of assessing the costs related to this disease. A detailed knowledge of the cost allocation would provide a solid basis on which health care priorities can be rationally set. Next to hospitalization, drug treatment accounts for the highest expense for direct medical costs of PD. Therefore, this analysis focuses on the costs of drug treatment for PD. The cost analysis was based on a retrospective study of 409 patients with PD who were seen over a 1-year period in our movement disorders clinic. The cost of therapy varied considerably depending on the severity of the condition (assessed in the "off" phase), the incidence of motor fluctuations, and the type of PD. In the early stage of the disease (Hoehn and Yahr stage I [HY I]), mean daily costs for therapy were DM (German marks) 6.60, which increased in later stages of the disease (HY V) to DM 22.00. If rare cases requiring continuous subcutaneous apomorphine infusion were included, mean daily costs of patients in HY V rose to DM 32.50 (the mean daily costs of subcutaneous apomorphine-treated patients in HY V: DM 74.30). Patients with motor fluctuations accounted for higher costs (DM 16.50) compared with those without motor fluctuations (DM 7.80). With respect to the three subtypes of PD, the mean daily expenditure was DM 7.00 for the tremor-dominant type, DM 12.40 for the akinetic-rigid type, and DM 10.80 for the mixed type. In the group of 409 PD patients included in this analysis, the average daily expenditure for drug treatment totaled DM 10.70 per patient (including patients on subcutaneous apomorphine).