21 hematology centers in Turkey will participate in this noninterventional observational study. The recruitment target is 960 cases. Patients will be followed-up at least 1 year or to the end of the study according to the physicians' discretion, or withdrawal of consent. Recruitment period will be 36 months. Data will be collected via electronic case report form. Since the study cohort does not include only newly diagnosed patients, all aTTP patients will be included to the study, previous treatments and diagnosis information data could also be collected from hospital records. Patients recruitment duration: 3 years (36 months) Patients follow-up duration: 1 year (12 months)