STUDY OBJECTIVES: To evaluate an association between catechol-O-methyltransferase (COMT) genotype and subjective daytime sleepiness in patients with Parkinson disease. DESIGN: Structured questionnaire study. SETTING: Tertiary Parkinson disease care center and sleep outpatients' department at the university hospital neurology department. PARTICIPANTS: All nondemented patients with idiopathic Parkinson disease who had been part of a previous study of D4-receptor polymorphisms in 1997 were eligible to participate. From the original sample of 113 patients, 46 participated in the study, 22 met exclusion criteria, and 43 were not available. INTERVENTIONS: Not applicable. MEASUREMENTS AND RESULTS: In this study, 46 patients were included (27 men, 19 women; 68.4 +/- 9.9 years of age; symptomatic disease duration, 12.2 +/- 5.2 years; Hoehn and Yahr stage in "on" of 2.6 +/- 0.8). Out of the 46 patients, 13 had LL genotype, 22 LH, and 11 HH. The Epworth Sleepiness Scale scores were 9.5 +/- 4.8 in LL, 8.5 +/- 4.7 in LH, and 6.8 +/- 3.1 in HH (mean +/- SD) (NS). LL and LH were grouped together. The Epworth Sleepiness Scale score was 11 or more in 40% of the LL+LH group, compared to 9.1% of the HH group (P = .039). The levodopa or dopamine-agonist doses and types did not differ between the LL+LH group versus the HH group. CONCLUSIONS: These preliminary data suggest an association of the Lallele and daytime sleepiness in patients with Parkinson disease.