Obstructive Sleep Apnea (OSA) is the most common sleep-related breathing disorder, representing a major socioeconomic burden on healthcare systems worldwide. Studies performed in Europe in the last twenty years showed a very high prevalence and highlighted that the severity of untreated OSA worsens over time. OSA is associated also with an increased risk to develop cardiovascular, cerebrovascular and metabolic diseases. Finally, recent studies reported a very high mortality in untreated OSA patients, including those with mild severity. Data on European population have been obtained by the ESADA group (European Sleep Apnea Database) , a consortium of 25 sleep center across Europe that includes three Italian Research Hospitals. The ESADA showed significant differences between European geographical macrozones in terms of symptoms and complications. However, no data are available for the Italian population in terms of prevalence, clinical presentation and comorbidities. The present project aims to overcome this limitation by obtaining a more defined picture of OSA in Italy. A cohort study was designed in collaboration with the Sleep Centers endorsed by the Italian Scientific Society of Sleep Medicine (AIMS). Aims of the present project are to: 1. Assess the distribution different physiological (endotypes) and clinical patterns (phenotypes) of OSA in Italian patients 2. Analyze the association between OSA and co-morbidities 3. implementation of an Italian database for long-term follow-up studies. Methods * Clinical, sleep study and treatment data will be collected for each patient. A clinical questionnaire will be developed in order to standardize the clinical data collection; to this end a feasibility study will be performed on 100 patients (25 pts for Coordinator/HUB center). * Excessive daytime Sleepiness, Neurocognitive, anxiety/depression screening * A web-based data collection platform will be designed to store pseudo-anonymized individual data. OUTCOMES 1. Distribution of OSA severity in Italy according to the different classification methods 2. Definition of metabolic, cerebro- and cardiovascular risk factors prevalence associated with OSA in Italian Population 3. Distribution of different physiological and clinical patterns and their association with co-morbidities 4. Definition of a screening/case finding questionnaire for Italian Population 5. Definition of an ongoing cohort of patients that will be followed-up 6. Implementation of an OSA registry that will be shared with Italian Health System or Agencies to designed preventive or early diagnosis interventions to reduce the health impact of the disease.