Automobile accidents are reported as being overrepresented in those suffering from the obstructive sleep apnea syndrome (SAS), evident by snoring, sleep disturbances and diurnal hypersomnia. An estimation of the prevalence of these symptoms amongst an adult population, predominantly automobile drivers, was assessed by using a one-stage questionnaire procedure. From a national random sample of 1214 persons a weighted reply rate of 76% was achieved. Snoring, breath cessations, mid-sleep awakenings, and diurnal hypersomnia were reported in 24, 3.8, 27 and 9.1%, respectively. The maximum prevalence of SAS was estimated as 2.8-5.5% among men, aged 30-69 years, depending on definition used. Driving frequency in potential sleep apneics was similar to that of the entire population studied. Diurnal hypersomnia, considered a consequence of SAS, was reported as an overall 2.2%, corresponding to 100,000 automobile drivers in Sweden.