We compared serum levels of coenzyme Q10 and the coenzyme Q10/cholesterol ratio in 33 patients with Parkinson's disease (PD) and 31 matched controls. The mean serum coenzyme Q10 levels did not differ significantly between the 2 study groups. Coenzyme Q10 levels were not correlated with age, age at onset, duration of the disease, scores of the Unified Parkinson Disease Rating Scale (UPDRS) or the Hoehn and Yahr staging in the PD group. The coenzyme Q10/cholesterol ratio had a significant correlation (although low) with duration of the disease (r = -0.46), total UPDRS score (r = -0.39), motor examination of the UPDRS (r = 0.45). These values were not influenced significantly by therapy with levodopa or dopamine agonists. The normality of serum coenzyme Q10 and coenzyme Q10/cholesterol ratio suggest that these values are not related with the risk for PD.