To investigate the daytime sleepiness in patients with sleep apnea syndrome, we used a test for measurement of sustained attention. The present study was performed on 65 participants: 10 healthy non-snoring volunteers, 25 snoring volunteers and 30 patients with symptoms of sleep apnea. The error rate (percentage of incorrect responses) appears to be most suitable for the evaluation of the test. The difference between the habitual snorers and the healthy non-snoring volunteers was statistically significant. At the apneic patients, there are significant differences in age, sex, and body mass index; attention decreases significantly in the last 10 minutes of the test. The attention test can be helpful for the measurement of daytime sleepiness in apneic patients.