Delayed diagnosis in patients with Churg-Strauss syndrome (CSS) is largely attributed to the variable and nonspecific presentation of the disease's initial symptoms. The aim of the study was to evaluate the effect of delayed diagnosis on the course of CSS. We conducted a retrospective study of 30 CSS patients followed up in our department. In each patient, we assessed the delay in CSS diagnosis (the time when patients already fulfilled four out of six of the American College of Rheumatology criteria and the diagnosis was not yet established), the disease activity at the time of diagnosis, and organ involvement during CSS course. A median value of 2 weeks was chosen as the cutoff point after which the diagnosis was considered as delayed. Sixteen patients were diagnosed before (group 1) and 14 patients after this cutoff point (group 2). In group 2, we found a higher Birmingham Vasculitis Activity Score at the moment of diagnosis (20.4 vs 25.1, p < 0.05) and a more severe disease course, resulting in more frequent hospitalization rates (0.64 vs 2.26/year, p < 0.00001), higher corticosteroids dose requirements (5.87 vs 11.57 mg/day converted to methylprednisolone, p < 0.0001), and additional immunosuppressive therapy administration (56.2 vs 92.8 %, p < 0.05) to maintain disease remission. All six perinuclear pattern of antineutrophil cytoplasmic antibobodies (pANCA)-positive patients (20 %) were found in group 1. Concluding, the delay in diagnosis of CSS of more than 2 weeks was found to be associated with a disease course that was more severe. The presence of the pANCA antibodies may occasionally facilitate establishment of the diagnosis.