Objectives: The aim of this study is to evaluate the remedial effect of continuous positive airway pressure (CPAP) therapy on neurocognitive function in obstructive sleep apnoea (OSA) patients. Methods: The cognitive impairment in OSA patients was evaluated with Montreal Cognitive Assessments (MoCA) before and after CPAP therapy. The study assessed 54 patients who were diagnosed with OSAS seen at the neurology clinic of the Trakya University Medical Faculty. They were given MoCA the day of diagnosis, after one day of CPAP therapy, and after three months of CPAP therapy. Results: MoCA scores before treatment showed a statistically significant correlation between disease severity and abstract thinking (Correlation coefficient: 0.270±0.048). There was no significant difference between MoCA scores before treatment and after one day of CPAP therapy (p=0.244). However, there were significant improvements in MoCA scores after three months of treatment, when compared to scores from before treatment and after one day of therapy (p<0.001). Conclusions: CPAP treatment may improve cognitive function in OSA patients. MoCA is an effective and simple tool for evaluating cognitive function.