Concern has been raised in the medical literature that the use of leukotriene receptor antagonists for the treatment of asthma may be associated with an increased incidence of Churg-Strauss syndrome, a rare small-vessel vasculitic syndrome. This review provides a critical appraisal of the literature to address this question. The incidence of Churg-Strauss syndrome in the general population is one to four cases per million. In patients with asthma it is 20-60 cases per million patient-years, which is similar to that seen in a population receiving leukotriene receptor antagonists. There is no evidence for a direct causative role of leukotriene receptor antagonists in the development of Churg-Strauss syndrome. There may be multiple other non-causative reasons for an association, including the fact that these agents may be initiated in patients who are already in the process of developing Churg-Strauss syndrome, or that the use of leukotriene receptor antagonists leads to a reduction in corticosteroid use, which in turn allows the Churg-Strauss syndrome to be 'unmasked'.