In several studies by Henrard et al, in vivo recovery (IVR) has been shown to be significantly higher in overweight and obese patients with haemophilia than in normal weight patients.3–5 In addition, weight-adjusted clearance decreases with age, whereas weight-adjusted volume of distribution does not.6 The latter suggesting that weight-adjusted volume of distribution is constant over time.3 4 6 We set out to further prove this assumption by describing the impact of extreme weight loss on FVIII pharmacokinetic (PK) parameters in haemophilia A, which has not been done earlier. This evidence concerns the gene F8 and hemophilia A.