The aim of this prospective longitudinal study of patients treated for generalized aggressive periodontitis (GAP) was the clinical, microbiologic, and radiologic longitudinal evaluation of implants placed into bone regenerated by the guided bone regeneration (GBR) technique. Ten patients with GAP who had lost either one or two maxillary incisors or premolars through periodontal disease and whose alveolar bone was neither high nor wide enough for implant placement were enrolled in the study. GBR was carried out in a two-stage procedure using titanium-reinforced extended polytetrafluoroethylene membranes and titanium screws. No bone graft or bone substitute materials were used. After 6 to 8 months, the membranes and supporting screws were removed, and a total of 15 implants (Nobel Biocare) were placed. The control group comprised 10 periodontally healthy patients who had a total of 11 implants (Nobel Biocare) placed in the maxilla (incisor and premolar region) without GBR because of aplasia, trauma, or endodontic lesions. All patients were examined 2 to 4 weeks before extraction of the nonretainable teeth (baseline) and again immediately after placement of the superstructure. Further examinations were performed within the framework of a 3-month recall schedule over a 3-year period. At each session, clinical parameters (probing pocket depths, bleeding on probing, gingival recession, clinical attachment level, Gingival Index, and Plaque Index) were recorded at teeth and implants, and the composition of the subgingival microflora was determined by dark-field microscopy and DNA probe. Intraoral radiographs were taken for control purposes at baseline, immediately after insertion of the superstructure, and 1 and 3 years later. The GBR technique yielded a horizontal and vertical bone gain of 4.5 to 7.0 mm in the GAP patients. The clinical, microbiologic, and radiologic findings indicated healthy periodontal and periimplant conditions in both patient groups throughout the study. However, a slightly increased attachment loss (0.65 mm) and bone loss (1.78 mm) were recorded at the implants in the regenerated bone after 3 years of loading. The 3-year implant survival rate was 100% in both groups. The possibility of continuous attachment loss and bone loss occurring at teeth and implants in regenerated bone cannot be ruled out in patients treated for aggressive periodontitis. The prognosis for the retention of the teeth and implants is thus open to question.