Haemophilia A (HA) is an X-linked bleeding disorder that results from coagulation factor VIII deficiency. Residual factor VIII activity levels (FVIII:C) largely reflect F8 gene mutations and are used to classify HA as severe (<1%), moderate (1–5%) or mild (>5%). However, FVIII:C may differ among individuals carrying the same F8 mutation.1 Furthermore, bleeding phenotypes and FVIII:C can be discordant,2 which poses a particular challenge for mild/moderate individuals.3 Identification of variants in additional genes involved in haemostasis is important for improving classification and treatment guidelines for individuals with HA. Here, we describe four related males carrying F8 mutation c.494C>T (p.Pro146Leu) with moderate FVIII:C levels. However, clinical severity differs: two are mild and two are severe. The aim of this study was to identify gene variants in these individuals that may explain discordant bleeding phenotypes.