Background: Sickle Cell Disease (SCD) is a severe, potentially life threatening hereditary hemoglobin disorder requiring multidisciplinary care including screening, prevention, health education and management of acute and chronic complications. [ME Houwing et al, Blood Rev 2019] Although it affects millions of people throughout the world mainly individuals of African descent, Mediterranean (Caucasian) and Asiatic population, global migration from regions where the disease is endemic are changing its geographical distribution with a significant impact on patient survival, quality of life and costs for health systems requiring new treatment and preventive approaches. Data on epidemiological and clinical profiles of SCD have deeply changed also in Italy, a country with a high prevalence of hemoglobinopathies and where SCD is already present in the native population, due to an increasing number of immigrants from countries with high disease prevalence. Currently, approximately 2,000 SCD patients live in Italy. The creation of an Italian National Registry of Thalassemia and Hemoglobinopathies - was approved in 2017 thanks to a strong joint initiative of the Italian Society of Thalassemias and Hemoglobinopathies (SITE) and national patients associations. However the Registry is not yet completed, thus, the information currently available is very limited. [G Russo et al, Orphanet J Rare Dis. 2019] The Italian National Health Service is organized in Regions and Local Health Units (LHU). Each LHU reimburses health providers (eg, public and private hospital, general practitioners, outpatient services providers) for health assistance provided to citizens referring to the LHU, and uses specific databases to track the health assistance provided containing useful data to describe the type of assistance (eg, patient beneficiary, date of assistance) and to calculate the related charge. The main purpose of GREATalyS trial (CSEG101AIT01) is to collect data on SCD which may be representative of the national picture to better understand the burden of illness in terms of patient population, key disease features and resources consumption in Italy. Methods: Observational retrospective analyses will be carried out by integrating administrative databases for healthcare resources consumption (pharmaceuticals database, hospitalizations database, diagnostic tests and specialist visits database) from a sample of Italian Regions and LHUs, geographically distributed across the National territory (balanced between regions and number of covered residents). A representative sample of the whole national landscape through the involvement of approximately 11 LHUs and Regions will allow capture of approximately 23 million covered residents, representing about 38% of the entire Italian population. Patient Socio-Demographic characteristics (age, gender), all hospitalizations (SCD related and not related), previous SCD treatment type, co-morbidity profiles, patient treatment patterns, resources use and health services cost will be collected and analyzed. Anonymized patient data will be extracted into the Hospitalization database searching the relevant International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM codes). All analyses will be performed by STATA SE, version 12.0. The Local Ethics Committee of each participating Region/LHU has been notified about the study. Objectives: Composite objectives will collect both epidemiological and burden of illness data. Primary study objective is to estimate SCD prevalence and incidence rate from January 2010 to December 2018. Key secondary objectives include description of demographic and clinical characteristics, therapeutic pathways, health care resource use and direct costs (derived from health care resource utilization in term of drug treatments, diagnostic tests, specialist visits and hospitalizations) for patients affected by SCD. Conclusions: GREATalyS is to our knowledge the first SCD real world evidence study in Italy leveraging National Health System administrative databases to collect epidemiological and burden of illness data, and represents a useful health assessment model to better understand the evolving scenario in Italy, a country where SCD is becoming an emerging health problem. Figure Disclosures Castiglioni: Novartis Farma SpA: Employment. Condorelli:Novartis Farma SpA: Employment. Amore:Novartis Farma SpA: Employment. Perrone:CliCon srl: Employment. Alessandrini:CliCon srl: Employment. Veronesi:CliCon srl: Employment. Degli Esposti:CliCon srl: Employment. Premoli:Novartis Farma SpA: Employment. Fiocchi:Novartis Farma SpA: Employment.