The aim of this investigation was to assess the role of supportive periodontal care in the maintenance of clinical attachment gained, after surgical treatment according to the principles of GTR, in deep infrabony defects. Following GTR treatment, 40 deep infrabony defects in 23 patients gained 4.1 mm of probing attachment level (PAL) after 1 year of stringent plaque control. In the subsequent 3 years, 15 patients (22 sites, group A) were recalled every 3 months. In this group, the gained attachment level remained stable. Conversely, 8 patients (18 sites, group B), who received only sporadic care, lost at 4 years, 2.8 +/- 2.7 mm of the PAL gained at 1 year. Group A patients had significantly lower full mouth plaque and bleeding scores than group B at 4 years. Furthermore, detection of bleeding on probing, plaque, P. gingivalis and P. intermedia was significantly more frequent in regenerated sites of group B patients. Risk assessment analysis indicated that GTR sites in patients receiving only sporadic care had a 50-fold increase in risk of PAL loss between 1 and 4 years with respect to patients undergoing regular recall. It was concluded that stability of gained clinical attachment was dependent upon stringent oral hygiene.