Background/aim: The aim of this study was to investigate the effects of conscious sedation with 40% nitrous oxide/oxygen (N2O/O2) on cognitive functions. Materials and methods: Forty dental patients referred to the sedation unit at Gazi University Faculty of Dentistry Department of Oral and Maxillofacial Surgery received a combination of 40% N2O/O2 inhalation for conscious sedation. Psychometric tests were applied three times: before sedation, during sedation, and at the end of the recovery, for assessing cognitive functions. Results: The results of this study showed that the 40% N2O/O2 combination impaired cognitive functions during the conscious sedation. Recovery of most of the cognitive functions occurred 15 min after sedation. However, in addition to the persistence of 'hypnotic effects' and 'sensations of isolation' during the recovery period, 'motor loss value' showed more cognitive impairment 15 min after sedation than before the sedation period, and, thus, the ability to execute fine motor skills was not totally recovered by then. Conclusion: The results of this study could be crucial for informing patients about avoiding attentive activities soon after conscious sedation via 40% N2O/O2.