Excessive daytime sleepiness (EDS) is a common but underrecognized and preventable cause of traffic accidents. It creates a problem of particular importance for professional drivers. We performed the Epworth Sleepiness Scale (ESS) and questionnaire related to their history of traffic accidents to 118 professional taxi drivers to determine the EDS and its effects on driving performance in taxi drivers. There were 58 (49.2%) subjects with loud snoring, 8 (5.9%) subjects with cardinal symptoms due to obstructive sleep apnea syndrome (OSAS) and 28 (23.7%) subjects with ESS > or =10 in the group of taxi drivers. Eighty (67.8%) drivers had been involved in a traffic accident. We found a significant relation between the number of traffic accident and EDS, witnessed apnea, cardinal symptom related to OSAS but not with snoring. The present data that sleepiness is a common symptom in taxi drivers and may be related to traffic accident.