This study is a prospective, single center, observational, 2-cohort study of adult patients with severe Hemophilia A. There is no randomization procedure and all patients will be treated as per usual clinical practice. Patients will be followed up for 18 months after enrolment.

The primary therapy for hemophilia is coagulation factor replacement, given either episodically on demand (OD) for the treatment of acute bleeds or prophylactically to prevent them.

The last years there has been an interest to study the comparative effectiveness of OD vs. SP (Secondary Prophylaxis) treatment strategies so as to create an evidence based platform to guide both clinical decision making and quantify the economic aspects of each treatment alternative. In Greece relevant information is lacking, thus it is imperative to study how patients on different treatment strategies are managed in a real-life setting in Greece, including the main factors associated with increased health care utilization, clinical success and patient well being.

Inclusion Criteria:

• Patients diagnosed with severe Hemophilia A.
• Age ≥18 years old
• Patients able to read and write
• Patients receiving Factor VIII substitute therapy, either on-demand or as secondary prophylaxis.
• Patients under the same therapeutic strategy (On Demand or Secondary Prophylaxis) for at least 6 months prior to enrolment.

Exclusion Criteria:

• Patients that have developed inhibitors against factor VIII.
• Patients participating in an investigational program with interventions outside of routine clinical practice.

This will be a single center prospective two-cohort observational study conducted in a hospital setting.Patients will be enrolled from the biggest specialty management center in Greece