We describe the case of 18 year old twin brothers who presented to our unit with a 3 year history of aquagenic urticaria. This rare form of urticaria usually presents within an hour of contact with water. The aetiology is unknown. Most cases are sporadic but there are a small number of familial cases in the medical literature. A specific genetic mutation has not yet been found. To our knowledge, this is the first report of aquagenic urticaria in monozygotic twins, further supporting a genetic component to this disease.