The objective of the present study was to investigate the prevalence of insomnia and excessive sleepiness in relation to the presence and severity of obstructive sleep apnea (OSA). The sample consisted of patients referred to a university hospital on suspicion of OSA. In total, 1115 patients with mean age of 48 years were studied. Insomnia (Bergen Insomnia Scale) and excessive sleepiness (Epworth Sleepiness Scale) were diagnosed using validated questionnaires. The insomnia scale permits diagnosing insomnia using both old and new (from 2014) criteria. OSA was diagnosed and categorized based on a standard respiratory polygraphic sleep study using a type 3 portable monitor. OSA was diagnosed in 59.4 % of the referred patients. The prevalence of excessive sleepiness was higher with greater severity of OSA: 40.5 % in the patients without OSA (apnea-hypopnea index (AHI) <5), 46.5 % in mild OSA (AHI 5-14.9), 52.0 % in moderate OSA (AHI 15-29.9), and 58.0 % in severe OSA (AHI 30 or above). In contrast, the prevalence of insomnia using the 2014 diagnostic criteria showed an opposing prevalence: 54.2 % no OSA, 54.9 % mild OSA, 48.5 % moderate OSA, and 44.6 % severe OSA. Logistic and linear regression analyses showed that sleepiness was positively associated whereas insomnia was negatively associated with OSA severity and AHI. Both excessive sleepiness and insomnia were seen in high proportions of the patients referred on suspicion of OSA. Excessive sleepiness was higher whereas insomnia was lower with greater OSA severity.