We predicted that haemophilia would create a prohaemorrhagic host-parasite relationship, which would make haemophiliacs very vulnerable to haemorrhagic effects of intestinal helminths in tropical countries like Nigeria. If our prediction is correct, the frequency and risks of gastrointestinal haemorrhage and iron deficiency will be higher among haemophiliacs infected by helminths in comparison with uninfected haemophiliacs. Frequency of gastrointestinal haemorrhages and iron deficiency among haemophiliacs with and without intestinal helminth infections were retrospectively obtained and analysed, and their relative risk determined by regression analysis. Haemophiliacs with intestinal helminths had significantly higher frequencies of gastrointestinal haemorrhage (73.3% vs. 18.5%, p<0.05) and iron deficiency (60% vs. 22.2%, p<0.05) in comparison with haemophiliacs without intestinal helminths. Haemophiliacs with intestinal helminths had significantly elevated relative risks (RR) of gastrointestinal haemorrhage (RR=3.4, CI95%: 2.4- 4.3, p=0.007) and iron deficiency (RR=2.5, CI95%: 1.7-3.3, p=0.009). These results showed that helminth infections were associated with increased risks of gastrointestinal haemorrhage and iron deficiency in haemophiliacs. This is thought to be due to a pro-haemorrhagic host-parasite relationship resulting from host haemostatic abnormality, coupled with the concurrent manipulation of the host haemostatic system by anticoagulants produced by some of the parasites. Haemophiliacs in tropical countries should be regularly screened and treated for intestinal helminths.