The aim of this study assessment of OSAS role in occurrence of road traffic accidents in sleeping drivers of commercial heavy vehicles such bus and truck driver. This cross-sectional and case-control study was carried out on 760 truck and bus drivers that were involved in a road accident between 2009 and 2011 in Yazd - Iran. In this study we used the Polysomnography method for assessing patients with suspected sleep disorders, including sleep apnea. The stage of sleep is assessed by electroencephalography. The findings indicated that among 760 drivers, 91 drivers had more than 10 EES score. Among 91 drivers, 35 drivers involved in one accident and 38 drivers had no history of accident in study period. Driving in the night time had significant association with road accident occurrence in participated drivers (p=0.01). Drivers who have sleepiness and especially OSAS had more chance to involve an accident. But OSAS was not independent predictor of road accident.