In 1997 we evaluated answers to a sleep questionnaire in a representative sample of 1186 persons of adult population of Warsaw. In the year 2000 we sent the same questionnaire to all persons who participated in the 1997 investigations. 676 (57%) subjects responded. There were 53% males and 47% females in the studied group. Their mean age was 56.6 +/- 8 years. There was no difference in age and sex between responders and non-responders. The standardized questionnaire contained questions assessing the following items: snoring, excessive daytime sleepiness, apnoeas observed by the sleep partner, sleep time and sleep latency. During a 3-year follow-up mean sleep time on working days did not change and remained 7.1 +/- 1.1 h. However, the subjects slept significantly shorter time at weekends, 8.1 +/- 1.3 and 7.9 +/- 1.3 h respectively (p < 0.001). There was a decrease in percentage of snorers from 81% to 75% and increase in BMI from 27 +/- 4.5 to 29 +/- 5 kg/m2. The daytime sleepiness was reduced from 7.9 +/- 4.5 to 6.4 +/- 3.9 points (p < 0.001).