The aim of this thesis was to elucidate factors possibly contributing to the rapidly progressing periodontitis in a group of Papillon-Lefèvre syndrome (PLS) patients and to evaluate a combined mechanical and antimicrobial treatment model in these patients. The total patient sample consisted of 20 individuals referred to King Faisal Specialist Hospital and Research Centre in Saudi Arabia for treatment of PLS. Saliva samples were obtained from 16 patients with the diagnosis of PLS. A control group was selected from healthy siblings and healthy children and young adults from Saudi Arabia. Both the unstimulated and the stimulated whole saliva secretion rates were significantly lower in PLS-patients compared to control individuals (p<0.01 and p< 0.05). The buffer capacity was also significantly lower (p<0.01), whereas IgA and lactoferrin concentrations were significantly higher (p<0.01) in the PLS-group. A significantly lower output was detected for peroxidase when calculating the amount or activity per time among the PLS-patients compared to controls. Subgingival microbial samples were obtained from 36 sites in 12 PLS patients in order to assess the occurrence of 18 different microbial species. Actinobacillus actinomycetemcomitans and P. gingivalis were only infrequently encountered in high levels in the subgingival samples whereas B. forsythus, T.denticola, P. intermedia and C. rectus reached high levels (≥10 6cells) in more then 50% of all patients. The results of the study indicate that there is no specific profile of the subgingival microflora in PLS patients. Blood samples were obtained from all 20 PLS individuals and from an equal number of healthy volunteers. Natural Killer cells (NK cells) from the PLS subjects exhibited significantly reduced cytotoxicity against K562 cells compared to controls (p<0.0001). NK cell cytotoxicity was severely depressed and was the only finding that was consistent among all PLS subjects. To evaluate the effect of retinoid treatment on the periodontal health nine participants that had received systemic retinoid medication for different length of time were compared to nine PLS patients with no such medication. The clinical data revealed no obvious difference in periodontal conditions between the retinoid-medication-group and the non-medication-group. Nine dentate PLS patients were subjected to an intensive mechanical and antimicrobial treatment regimen. Extractions were performed of teeth considered untreatable and periodontal treatment was initiated with non-surgical treatment during 6 weeks.The patients were prescribed to use amoxicillin (250 mg twice/day) and metronidazole (250-500 mg three times/day). After the initial 6-week treatment period, all patients were scheduled for maintenance care every 3 months. In addition to this mechanical maintenance treatment, tetracycline (250 mg/day) was prescribed and used continuously for 1.5 years. For teeth erupting during the 3-year observation period no lesion ≥6 mm had developed in 5 patients. In 3 patients demonstrating an unsuccessful treatment result the periodontal disease progressed on existing teeth and developed on several teeth erupting during the observation period. The 5 patients presenting an excellent or good treatment result all complied with the antibiotic treatment. It was concluded that a combined mechanical and antimicrobial periodontal treatment may lead to preservation of a periodontally healthy and functional dentition over several years.