Objectives: The main aim of this study was to examine whether there is a relation between increased daytime sleepiness and severity of obstructive sleep apnea (OSA). Other aims were examine whether OSA is more common in men or women, whether there is a relation between body mass index and severity of OSA and whether there is a gender difference in excessive daytime sleepiness. Study Design: This is a cross-sectional study. Material and Methods: This study involved 25 patients who performed full-night polysomnography at the Clinic of Neurology of the Osijek Clinical Hospital Centre and were diagnosed with OSA. Polysomnography determined severity of OSA (AHI). Patient's demographic data and clinical features were collected with an anonymous questionnaire. Excessive daytime sleepiness was estimated with the Epworth and Stanford Sleepiness Scale. Results: There were 20 (80 %) male and 5 (20 %) female patients with OSA in this study. The Epworth Sleepiness Scale scores showed that 10 (40 %) patients suffer mild excessive daytime sleepiness, 6 (24 %) patients suffer moderate excessive daytime sleepiness and 8 (32 %) patients suffer severe excessive daytime sleepiness. Severity of OSA is significantly associated with increased daytime sleepiness and body mass index. Results showed no significant difference in excessive daytime sleepiness between men and women. Conclusion: Based on the results of this study we can conclude that there is a relation between increased daytime sleepiness and severity of obstructive sleep apnea (OSA). OSA is more common in men. There si also a relation between severity of OSA and body mass index. There is no significant difference in excessive daytime sleepiness between men and women.