Results following three modalities of periodontal therapy (subgingival curettage, modified Widman flap surgery, and pocket elimination or reduction surgery) in 78 patients over 8 years were compared for variations in pocket depth and clinical attachment level related to tooth types (maxillary molars, mandibular molars, maxillary biscupids, mandibular biscupids, maxillary anterior teeth, mandibular anterior teeth). The analysis was based on a classification of three severity groups according to initial crevice or pocket depth (Class I, 1-3 mm; Class II, 4-6 mm; and Class III, 7-12 mm) and with patient's means of measurements being the experimental units for the statistical analysis. Reduction in pocket depth and gain of clinical attachment for pockets 4 mm or deeper occurred following all three methods of treatment, and was well sustained over 8 years. No one modality of treatment was consistently superior to any of the other two with regards to sustained reduction of pocket depth and gain of clinical attachment. Surgical pocket elimination or reduction did not enhance the prognosis for maintenance of periodontal support in either moderate or advanced periodontal lesions anywhere in the mouth compared with more conservative modalities of treatment. In spite of prophylaxis and instruction in home care every 3 months, there was a slight progressive loss of attachment over time in areas of shallow crevices (1-3 mm).