PURPOSE: Patients with obstructive sleep apnea (OSA) commonly have cognitive complaints. There are few randomized studies that have examined neuropsychological effects of continuous positive airway pressure (CPAP) treatment in patients with OSA. In this double-blind trial, we examined if a 3-week CPAP treatment compared with placebo CPAP treatment has specific therapeutic effects on cognitive impairments in patients with OSA and if there are specific domains of cognitive impairments sensitive to 3-week CPAP treatment. SUBJECTS AND METHODS: Thirty-eight newly diagnosed patients with untreated OSA underwent neuropsychological testing before and after 3-weeks CPAP or Placebo CPAP treatment. The two treatment groups (therapeutic CPAP, and placebo-CPAP) were compared using repeated measures analysis of variance (ANOVA). RESULTS AND CONCLUSION: Impairments in neuropsychological functioning ranged from 2.6% to 47.1% before treatment. In response to 3 weeks of treatment, there was no significant time by treatment interaction for a global deficit score of neuropsychological functioning. Only the Stroop Color (number correct) test showed significant improvement specific to CPAP treatment. The study demonstrates the importance of further randomized placebo controlled studies in this area.