In about half of the severe haemophilia A cases, the disease is caused by an inversion that split the F.VIII gene into two parts separated by approximate to 300-400 kb. Herein, we show that in the Turkish population this inversion mutation accounts for 29% of 141 haemophilia A cases and 42% of severe cases. Most of the inversions are of the distal type (72%) whereas nine were of the proximal type (28%). Haplotype analysis using 4 markers in the F.VIII gene did not reveal a single haplotype associated with the inversion. However, the pre- valence of one haplotype: HindIII (-) - Int13 (CA)(20) - Int22 (CA + CT)(26) - XbaI (-) is higher in the inversion patients. Since founder effect is excluded for the inversion patients, our results suggest that some as yet unknown factor(s) may make these alleles more prone for the inversion. However, a bias due to the low number of studied cases cannot be excluded.