Inclusion Criteria:  Male participants of all ages with severe hemophilia A (FVIII ˂1%) or moderate hemophilia A with severe bleeding phenotype who:  had been on standard prophylaxis or PK-tailored prophylaxis with octocog alfa during at least 12 months prior to the study enrollment (150 participants) or who started Advate® treatment in 2021 (20 participants), is being treated with octocog alfa at the moment of enrolment with any of the above mentioned treatment modalities, and had been assigned octocog alfa provision in Federal reimbursement program 2021 Availability of participants' records sufficient for data collection according to the study objectives during the retrospective period of the study for participants who had been on standard prophylaxis or PK-tailored prophylaxis with octocog alfa during at least 12 months prior to the study enrollment Written informed consent provided by the participant or, in case of children below 14 years of age, by participant's parent or participant's legally acceptable representative.  Exclusion Criteria:  Failure to obtain the participant's written informed consent Participation in any interventional study of products for hemophilia or other hemostasis disturbances treatment during 12 months prior to the study enrollment for participants who has retrospective data collection period and during 12 months after the study enrollment for all participants.