Obstructive sleep apnoea syndrome (OSAS) is a frequent disorder; however, the prevalence of sleep-disordered breathing is not well known in many countries. The aim of our investigation was to assess the prevalence of sleep-disordered breathing (SDB) in a representative sample of the population of Warsaw. We studied 676 subjects (57.1% of the randomised cohort from the Monica II study). The sample comprised 356 males (52.7%) and 320 females (47.3%), whose mean age was 56.6 +/- 8.2 years (range 41-72 years). Mean number of apnoeas and hypopnoeas per hour of time in bed (AH) in males was 7 +/- 9.5 and in females 3.9 +/- 6.6 (P < 0.001). SDB (cut-off point AH > 5 or >10) was identified in 188 subjects (27.8%) and 97 subjects (14.3%), respectively. SDB was established twice as frequently in males as in females (respectively 36.5 versus 18.5%; P < 0.001 for AH > 5 and 19.8 versus 8.5%; P < 0.001 for AH > 10). A diagnosis of OSAS AH > 10 and Epworth Sleepiness Score > or =11 points was established in 51 subjects (7.5%). The prevalence of OSAS was nearly four times higher in males (40 subjects, 11.2%) than in females (11 subjects, 3.4%; P < 0.001). The severity of OSAS was similar in both sexes (AH: males 32.3 +/- 14.9 and females 31.4.1 +/- 15.4). Older age and male sex were predictors of SDB. SDB and OSAS were independent predictors of coronary artery disease after adjusting for age, sex, body mass index, neck circumference and smoking habit.