Objectives: Knee osteoarthritis (OA) is a widespread disease that increases in the elderly and is an important cause of morbidity. It is common knowledge that resting and nocturnal pain is rarely seen in patients with knee OA, however latest studies showed that it is not rare. Sleep disorders are thought to be related with nocturnal pain and it is shown that in patients with arthritis are more likely to develop sleep problems. Nocturnal pain is also related with depression and decreased quality of life. This study aims to evaluate sleep quality in patients with knee OA and to reveal the relationship between severity of knee OA, pain and sleep disorders and quality of life in female and male patients. Materials and Methods: This cross sectional study includes 41 volunteer patients (27 female,14 male) between 40-65 years with knee OA, who suffer from knee pain for more than 6 months, and the study includes patients with grade 2 and 3 OA according to the Kellgren-Lawrence classification. Patients were evaluated using Visual Analog Scale (VAS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Lequesne Index, Pittsburg Sleep Quality Index (PSQI), Beck Anxiety Inventory (BAI), Beck Depression Inventory (BDI) and Short form-36 (SF-36). Results: VAS, WOMAC, Lequesne index, PSQI, BAI and BDI scores were significantly higher in female subjects than in male subjects. Prevalence of good sleep quality was significantly higher in male patients. There was a positive correlation between WOMAC scores and VAS, BAI and BDI scores, but there was no significant relationship between total PSQI scores. There was a positive correlation between Lequesne index scores and VAS, total PSQI, BAI and BDI scores. A negative correlation was found between WOMAC and Lequesne index and SF-36. Conclusion: Severity of knee OA is found associated with pain, depression and anxiety, sleep quality and quality of life. It should be considered to manage knee OA to improve quality of life.