Summary The aim of this study was to assess with a stop task the inhibitory motor control efficiency – a major component of executive control functions – in patients suffering from sleep disorders. Twenty-two patients with untreated obstructive sleep apnea syndrome (OSAS) (mean age 46 ± 9 years; mean apnea–hypopnea index, AHI = 30 ± 20) and 13 patients with psychophysiological insomnia (mean age 47 ± 12 years) were compared with individually matched healthy controls. Sleep disturbances in the patient populations were clinically and polysomnographically diagnosed. The stop task has a frequent visual ‘Go’ stimulus to set up a response tendency and a less frequent auditory ‘Stop’ signal to withhold the planned or prepotent response. The stop signal reaction time (SSRT) reflects the time to internally suppress the ongoing response. SSRT was slower for the apneic patients than for their respective controls (248 ± 107 versus 171 ± 115 ms,anova, P <0.05) but not for the insomniac patients compared with their controls (235 ± 112 versus 194 ± 109 ms, NS). Moreover, in apneic patients, slower SSRT was associated with lower nocturnal oxygen saturation (r = −0.477, P <0.05). By contrast, neither apneics nor insomniacs differed from their matched controls for reaction times on Go trials. To conclude, unlike insomniacs, OSAS patients present an impaired inhibitory motor control, an executive function which is required in many common everyday life situations. Inhibitory motor control relies on the integrity of the inferior prefrontal cortex, which could be affected by nocturnal oxyhemoglobin desaturation in apneic patients.