This case history describes the course of disease in a 17-year-old boy with Ehlers-Danlos syndrome type III and early-onset periodontitis. Flow cytometric tests showed a reduced cell count in the specific immune system. Immunoglobulin concentrations in saliva and serum were within normal limits. Infection with T-lymphotropic viruses was excluded. The phagocytic capacity of the peripheral blood polymorphonuclear leukocytes was unimpaired. The anaerobic infection present in the early-onset periodontitis was treated with systemic antibiotic therapy and closed curettage. Following 14 days of this treatment, signs of acute inflammation subsided, and 18 months after therapy ended, a slight gain in clinical attachment was found, and bone growth was visible via radiology. However, a continuing lack of adequate oral hygiene represents a risk to the success of therapy in the long term.