Purpose The objective was to assess the effect of continuous positive airway pressure (CPAP) on symptoms of anxiety and depression in patients with obstructive sleep apnea (OSA). We hypothesized a decrease in symptoms at follow-up, but that improvement relied on CPAP adherence. Methods The sample comprised 468 patients (mean age 55.5 years (SD = 12.0), 72% men) with OSA who received CPAP at a Norwegian hospital. OSA was diagnosed according to standard respiratory polygraphy. Mean baseline respiratory event index (REI) was 28.4 (SD = 20.6). Symptoms of anxiety and depression were assessed prior to CPAP treatment and at follow-up after a median of 20 weeks, range 6–52 weeks, with the Hospital Anxiety and Depression Scale (HADS). Patients...