The term overlap syndrome (OVS) in sleep disorders is used to describe the association of obstructive sleep apnea syndrome (OSAS) with one of the following disorders: chronic obstructive pulmonary disease (COPD), asthma, cystic fibrosis and interstitial lung diseases. Because OSAS and COPD are seen together frequently, the term of OVS is often used for OSAS associated with COPD. In both OSAS and COPD, some abnormalities on the level of oxygen saturation occur during sleep. These abnormalities are much more serious in the OVS. Oxygen desaturation destroys the architecture of sleep and leads to the complications due to hypoxemia, which are normally seen in the late stage of each disease, occur in early stage. In this review, interaction of sleep and some of the lung diseases was discussed.