PURPOSE: The present study was performed to compare the treatment outcomes of non-surgical periodontal treatment according to the distribution of attachment loss of a given patient. METHODS: Forty-five patients with moderate to severe periodontitis were divided in two subgroups; Group I patients with teeth manifesting attachment loss of > or =6 mm at one or more sites on the buccal/labial aspect while maintaining an attachment level < or =5 mm at the lingual/palatal aspect, Group II patients with teeth manifesting an attachment level > or =6 mm at more than one site on the lingual/palatal aspect while maintaining an attachment level < or =5 mm at the buccal/labial aspect. The probing pocket depth, probing attachment level, tooth mobility, and chewing discomfort were recorded at baseline and 6 months examinations following non-surgical periodontal therapy. RESULTS: The buccal/labial surfaces of teeth with moderate to severe periodontitis in Group I patients demonstrated a greater amount of pocket reduction, gain of attachment level, and tooth mobility reduction than the lingual/palatal aspects of teeth examined in Group II patients. CONCLUSIONS: Within the limits of the present study, the patients demonstrating attachment loss > or =6 mm at buccal/labial surfaces responded better to the nonsurgical periodontal therapy than those demonstrating comparable attachment loss at lingual/palatal surfaces.