© 2014, Ankara University. All rights reserved.Interstitial lung diseases (ILD), are a group of diseases which can involve pulmonary interstitium, small airways, and vessels, and diffusely affect pulmonary parenchyma as a consequence development of inflammation, and fibrosis leading to respiratory failure, and finally death. Obstructive sleep apnea syndrome (OSAS) is a disorder which courses with its systemic outcomes, and increasing morbidity, and mortality when accompanied with other respiratory system diseases. Concomitancy of OSAS with other lung diseases including chronic obstructive pulmonary disease, asthma, ILD, cystic fibrosis is termed as ‘‘overlap syndrome’’. Because of characteristic feature of OSAS ie. recurrent oxygen desaturations during night hours, ILD-OSAS concomitancy accelerates progression of underlying lung disease. Therefore, in cases with ILD, early diagnosis, and treatment of comorbid OSAS conveys vital importance in that this approach improves quality of life of the patients, and slows down progression of the disease. In this review ILD-OSAS concomitancy will be analyzed from its various aspects.