The purpose of this case report was to describe the clinical long-term outcome, 11 years after periodontal therapy, of 2 siblings diagnosed with Papillon-Lefèvre syndrome. Sibling 1 was a 14-year-old boy with severe periodontal bone loss in his permanent dentition. Sibling 2 was a 7-year-old girl with mixed-dentition and also suffering from periodontal disease. Both were treated with a combination of nonsurgical and antimicrobial therapy. Annual re-evaluations were performed for 11 years. Both siblings improved their periodontal status, but a low level of compliance with treatment over time by sibling 1 resulted in further tooth loss and recurrent periodontal disease. Sibling 2 experienced good periodontal healing in her primary and, later, permanent teeth due in part to proper compliance with oral hygiene instructions. Periodontal health was achieved, and no tooth loss occurred during follow-up. Papillon-Lefèvre syndrome subjects can be successfully treated with nonsurgical/antimicrobial therapy, but treatment outcome could be related to age at diagnosis and compliance with oral hygiene procedures.