BACKGROUND: Anxiety and depression are common comorbidities of excessive daytime sleepiness (EDS). Sleep-related breathing disorders (SBD) and central disorders of hypersomnolence (like narcolepsy [NA]) are the most frequent causes of EDS. This study aimed to evaluate mood disorders in NA patients compared to the subjects with EDS due to SBD (SBD-EDS). METHODS: In a retrospective analysis, subjects with NA and SBD-EDS were compared. All subjects underwent overnight polysomnography. NA patients underwent also multiple sleep latency test. Epworth sleepiness scale (ESS), Pittsburgh Sleep Quality Index (PSQI), Becks questionnaire, and Zung depression scale were used to assess EDS, sleep quality, anxiety, and depression, respectively. RESULTS: We enrolled 24 NA and 41 SBD-EDS subjects. Values of PSQI and Zung scale were significantly worse in the SBD-EDS group than in NA patients (8.34±3.84 vs. 6.83±2.25, p=0.04; 46.86±12.69 vs. 40.81±11.27, p=0.03, respectively). Anxiety was significantly more frequent in SBD-EDS subjects compared to NA (63.4% vs. 37.5%, p=0.04). Out of all observed sleep-related indices, PSQI was the only factor, that significantly correlated with the measures of anxiety in both groups (NA: r=0.65, p=0.001; SBD-EDS: r=0.45, p=0.003) and with the measures of depression in NA subjects (r=0.51, p=0.01). In SBD-EDS group, measures of depression significantly correlated with PSQI (r=0.46, p=0.002), oxygen desaturation index (r=0.35, p=0.03), and ESS (r=0.5, p=0.001). CONCLUSION: Compared to NA, our results suggest significantly worse measures of depression and a significantly higher frequency of anxiety in the SBD-EDS population. Measures of anxiety and depression significantly correlated with quality of sleep in both groups.