This report deals with a chronic granulomatous process, superficially resembling actinomycosis, which we noted in 7 patients with cystic fibrosis. Five of the seven patients succumbed as a result of this rare complication. The lesion was found in the lung in all cases, but not exclusively, and was associated with Micrococcus pyogenes, var. aureus, or with Pseudomonas aeruginosa, singly or in combination. An awareness of this condition may lead to the diagnosis during life. The diagnostic criteria, histologic appearance of the lesion, and the clinical course of the patients with this complication is presented.