We evaluated the rate of automobile accidents and daytime sleepiness using the Epworth sleepiness scale (ESS) in 44 patients with obstructive sleep apnea syndrome (OSAS). We defined the automobile accident score as a sum of two points for every one automobile accident and one point for every near-miss accident. Automobile accidents and near-misses were found in 54.5% and 50.0% in patients with OSAS. Automobile accident score was significantly correlated with the ESS score (r=0.56, P < 0.01). Our findings suggest that ESS score may be useful in detecting patients with the potential risk of automobile accidents associated with daytime sleepiness.