Churg-Strauss syndrome (CSS) is characterized by asthma, hypereosinophilia, and vasculitis involving at least two extrapulmonary organs.Churg-Strauss syndrome (CSS) is characterized by asthma, hypereosinophilia, and vasculitis involving at least two extrapulmonary organs.We report a case of a patient with antineutrophilic cytoplasmic antibody-negative CSS who developed pulmonary interstitial fibrosis (PIF).Churg-Strauss syndrome (CSS) is characterized by asthma, hypereosinophilia, and vasculitis involving at least two extrapulmonary organs.We report a case of a patient with antineutrophilic cytoplasmic antibody-negative CSS who developed pulmonary interstitial fibrosis (PIF).The possible relations between CSS and PIF are discussed. Because this case report is the first to describe features of pulmonary fibrosis in a patient with CSS, we cannot know whether this association is causal or fortuitous.