To the Editor: Eosinophilic fasciitis (EF) is an uncommon disorder with no documented prevalence and with unknown etiology. We describe a case of siblings with EF and identical HLA types, suggesting a genetic predisposition. The reporting of unique cases such as these is important in furthering our knowledge of rare conditions. Patient 1 presented at 14 years of age with a 3-month history of upper limb joint stiffness and swelling after prolonged physical exertion with associated general malaise and weight loss. On examination she had skin thickening with digital sparing and venous guttering predominantly of her upper limbs. Decreased range of movement of her wrists and metacarpophalangeal joints was noted. Total white blood cell count (WCC) was normal with an eosinophilia of 1.38 × 109/l (normal 0.04–0.44 × 109/l), an elevated serum immunoglobulin G (IgG) of 29.4 g/l (normal 5–13 g/l), and erythrocyte sedimentation rate (ESR) 42 mm/h. C-reactive protein … Address correspondence to Dr. Sullivan, 13 Larkfield Way, Lucan, County Dublin, Ireland. E-mail: sullivancat{at}yahoo.com