The clinical and morphologic features in 15 patients with bronchocentric granulomatosis were reviewed. Patients were divided into two groups on the basis of the morphologic findings. Group I consisted of five patients with necrotizing granulomas containing abundant eosinophils in the areas of necrosis. Three of these patients were asthmatic, two had elevated blood eosinophil counts, and in one there were fungal hyphae within necrotizing granulomas. In another case a sputum culture was positive for Aspergillus. The findings in these cases support the contention that some bronchocentric granulomas associated with tissue eosinophilia may represent a hypersensitivity reaction to inhaled Aspergillus. Group II included 10 patients with bronchocentric granulomas showing many polymorphonuclear cells but few eosinophils. One of these 10 had asthma, and blood eosinophilia was found in only one patient. The etiology and pathogenesis of these bronchocentric granulomas in unclear. The differences in morphology and clinical symptomatology between the two groups suggest that these lesions may arise from more than one etiologic agent and pathogenetic mechanism. Follow-up information was available for 11 individuals. Corticosteroids were given to four patients and lesions were resected from five patients. Neither recurrence of bronchocentric granulomas nor death due to them was reported.