Summary. Neutralizing inhibitors develop in 20–30% of patients with severe factor VIII (FVIII) deficiency. It is well established that Blacks have a higher prevalence of inhibitors than Whites. This is the first study to definitively demonstrate increased inhibitor prevalence in the Hispanic population. We compared inhibitor prevalence among various racial and ethnic groups in a cross-sectional analysis of 5651 males with severe haemophilia A that participated in the Universal Data Collection project sponsored by the Centers for Disease Control and Prevention. We used logistic regression analysis to control for potential confounding variables. We assigned as Hispanic those participants who were white and labelled themselves Hispanic. The prevalence of high-titre inhibitors in the Hispanic participants was 24.5% compared to 16.4% for White non-Hispanic patients (OR 1.4, 95% CI 1.1, 1.7). Possibilities as to the underlying cause of increased inhibitor prevalence in minority ethnic populations include polymorphisms in the FVIII molecule, HLA subtypes and differing inflammatory responses. A better understanding may lead to tailored treatment programmes, or other therapies, to decrease or prevent inhibitor development.