Churg-Strauss syndrome is a systemic necrotizing vasculitis involving small and medium-sized vessels. Classic features include asthma and hypereosinophilia. Antineutrophil cytoplasm antibodies (ANCA) are detected in about 40% of patients. Churg-Strauss syndrome has been reported in patients receiving leukotriene modifiers for asthma, in particular, leukotriene receptor antagonists (LTRA) (montelukast, zafirlukast or pranlukast). Clinical manifestations cases do not differ in these cases from those in Churg-Strauss syndrome without antileukotriene exposure. It is increasingly less likely that LTRA is the direct cause of this syndrome in those patients, although this hypothesis has not been completely ruled out. In many patients, LTRA treatment is prescribed because of worsening asthma, which is an early sign of Churg-Strauss syndrome. LTRA for asthma patients should be prescribed with great care, especially in cases of atypical or rapidly aggravated asthma. The onset of Churg-Strauss syndrome in patients treated with LTRA usually requires that they stop this treatment. Prescription of LTRA In patients with Churg-Strauss syndrome should be discussed with specialists.