The following communication is a case history of an 11 year-old female patient suffering from Papillon-Lefèvre syndrome. Since a massive occurrence of A. actinomycetemcomitans had been found in the subgingival microflora of the periodontal pockets, the patient was treated with repeated subgingival scaling, with an adjunct Amoxicillin and Metronidazol treatment. A bacteriological examination of the girl's family proved that several brothers and sisters as well as one parent also carried. A. actinomycetemcomitans, showing 3 different strains of this bacterium within the family. An immunohistological examination of the gingival tissue showed a massive inflammatory infiltrate which was dominated by plasma cells. The histological investigation of the first molars did not show morphological abnormalities of the root cementum. Posttreatment clinical and radiographical improvement of the periodontal conditions is reported despite the recurrent finding of A. actinomycetemcomitans.