The oral conditions of 42 patients being treated for cystic fibrosis were evaluated. The patients were grouped by age and, in some aspects, were compared with a small control group of their siblings. The patient group had a lowered incidence of plaque and less gingival disease than did the control group in which every person had some amount of plaque or gingival disease. Calculus formation was minimal. The reasons for the finding of minimal plaque in the patient group could be related to several factors, including the life-long use of various antibiotic agents, the chewing of digestive enzyme supplements, the effect of medical management on tooth hardness, and the effect of stained teeth (possible tetracycline deposition) on the plaque microorganisms. It appears that the therapy for cystic fibrosis was beneficial to the periodontal health of these patients. Much further study is needed to understand the interrelationship between an altered oral environment (salivary changes in cystic fibrosis), altered microbial flora (by antibiotics, enzymes) and even altered tooth surfaces (possible tetracycline deposition). Most patients were found to have one or more oral habits. Tooth mobility was associated with tension habits. Patients who had clubbed fingers (indicating pulmonary compromise) and possibly a severe disease process, did not appear to have either stained teeth or the severity of the gingivitis associated with this. The relationship of tetracycline to tooth staining could not be pinpointed.