The development of prepubertal periodontitis in Papillon-Lefévre syndrome (PLS) has been studied in 2 siblings, 12 and 8 years of age, since they were 5 and 3 years of age, respectively. Results of the treatment which comprised mechanical and chemical plaque control as well as systemic tetracycline medication, are reported. Extraction of temporary teeth, resulting in edentulousness prior to eruption of permanent teeth in the youngest child seemed to prevent destructive periodontitis from developing in the permanent dentition. After institution of continuous tetracycline medication in the oldest child at the age of 10 years, periodontitis with attachment loss did not occur in new sites. The possible rôle of specific micro-organisms in the progression of PLS-periodontitis is discussed.