Background: Sleep disturbance is closely related to inflammation and pain. Good sleep quality is essential for patients’ psychological and physical states as well as their quality of life. The aim of this study was to detect how insomnia as a major sleep disturbance could add to the disease burden in rheumatoid arthritis (RA) and osteoarthritis patients (OA) and to determine the predictor parameters in each of them in order to orient the rheumatologist to this unnoticed symptom that could adversely affect the patients’ life. This study included: 20 RA patients, 20 primary knee OA patients together with 20 healthy controls. RA disease activity was assessed by the disease activity score(DAS-28). All participants were assessed for sleep disturbances by the Athens Insomnia Scale, quality of life (QoL) using the short form QoL (SF-36 QoL) scale, depression by the Beck depression inventory (BDI), and functional disability by the Health Assessment Questionnaire Disability Index (HAQ-DI). OA patients were assessed by the Knee OA Flare Up Score (KOFUS) and the Western Ontario and McMaster Universities Arthritis Index (WOMAC).Radiological evaluation for RA patients was done by the Simple Erosion Narrowing Score, while the Kellgren & Lawrence (K-L) radiological grading system was used for OA patients. Results: Insomnia was found in 75% of the studied RA patients, 25% of the studied OA patients and none of the healthy control with significant difference (P