Following the performance of the POTTER observational study, whose primary objective was to collect data on the benefits of secondary prophylaxis versus on demand treatment in terms of prevention of bleeding episodes, the present study aims to extend the observation time up to 10 years, of the same population involved in the previous study.

The present study has been designed to allow a focus on long term disease-related damage at joint level in subjects with severe haemophilia A, as well as on the pharmacoeconomics impact of the two different treatment regimens.

Inclusion Criteria:

• Completion of follow-up in the original Potter study without having being excluded from the Intention To Treat efficacy analysis of the primary endpoint;
• Written informed consent specifically issued for the 5-year extension.

Exclusion Criteria:

• Switching of treatment to a Factor VIII concentrate different from Kogenate Bayer/Helixate NexGen after the end of the previous follow-up period.

A total of approximately 50 patients with a diagnosis of severe haemophilia A (FVIII < 1%) , who are already on Kogenate Bayer treatment ongoing for long-term secondary prophylaxis or on-demand therapy and have properly completed the follow-up in the original Potter study are expected to be enrolled.