Chronic synovitis affects about 10% of patients with severe haemophilia in India. This disease has some features in common with ankylosing spondylitis, which has been linked to HLA B27. We therefore aimed to test whether there is an association between HLA B27 and chronic synovitis. We studied 473 patients with severe haemophilia (33 of whom had chronic synovitis), and 1175 healthy controls using a standard serological technique and the reverse line strip assay. 64% (21 of 33) of patients with haemophilia and chronic synovitis were positive for HLA B27, compared with 5% (23 of 440) of those with severe haemophilia, but not chronic synovitis (odds ratio 31.6 [95% CI 9.28-39.38], p<0.0001), and 9% (100 of 1175) of healthy controls (18.81 [9.6-27.7], p<0.0001). We conclude that there is a strong association between HLA B27 and chronic synovitis in Indian patients with severe haemophilia and screening in this population could allow treatment and prevention of the complication.