Emerging evidence suggests that sleep-related disturbances such as sleep-disordered breathing (e.g. sleep apnea), sleep fragmentation, abnormal sleep architecture, and periodic limb movements (PLMs) are closely linked with adverse health outcomes such as cardiovascular events, hospital admissions and mortality. However, data supporting some of these associations is inconclusive. The Sunnybrook Health Sciences Centre sleep clinic has collected a detailed set of physiological variables from adults who underwent daytime and overnight sleep studies at the Sunnybrook Health Sciences Centre Sleep Laboratory from 2004 till present. Data exists on more than 5,000 subjects with various disturbances of sleep. The investigators plan to link the Sunnybrook Sleep Laboratory data with various health administrative databases based at the Institute for Clinical Evaluative Sciences (ICES). The primary objective of this study is to determine whether the presence of various findings on polysomnography (e.g. obstructive sleep apnea, sleep structure / fragmentation, physiological characteristics such as arousals and periodic limb movements in sleep) are associated with different adverse health outcomes such as cardiovascular events, cancer, depression, hospital admissions, emergency department visits and mortality.