The study was undertaken to investigate whether a long-term CPAP therapy improves the symptoms of daytime sleepiness in patients with the obstructive sleep apnoea syndrome. Seventy six patients (72 men and 4 women) with AHI = 53(+/- SE = 3), BMI 35 (+/- SE = 0.8), mean age 46.3 (+/- SE = 11.4) have undergone CPAP therapy for at least one year (mean: 2.48 +/- SE = 0.33). The aggravation of alterations of the daytime sleepiness was estimated using the questionnaire from Sleep Laboratory at the Marburg University and the Epworth Sleepiness Scale (ESS). After the CPAP therapy, we have observed the decrease of the symptoms of the excessive daytime sleepiness (p < 0.001). Negative correlation between CPAP compliance and ESS outcome was observed (r = 0.4; p < 0.001). There was not correlation between the term of using CPAP and the degree of the complaints decrease.