Purpose: The aim of this cohort study was to evaluate the width of keratinized mucosa at implant sites of partially edentulous patients who were treated for generalized aggressive periodontitis. Materials and Methods: Dental implants were placed in 35 patients who were treated for generalized aggressive periodontitis and 18 periodontally healthy individuals (controls). At baseline, the keratinized mucosa of all implants was ≥ 2 mm. Follow-up examinations were conducted every 3 months over a 4-year period. Results: The implant survival rate was 97.3% in patients with generalized aggressive periodontitis and 100% in the control group. Four years after implant insertion, patients with generalized aggressive periodontitis had significantly higher clinical attachment levels at the teeth and implants compared with the controls. At all time points, in both groups the mean probing depth at the implants was significantly larger than at the teeth. The mean widths of keratinized mucosa and keratinized gingiva were not significantly different between the two groups. In both groups, the widths of keratinized mucosa and keratinized gingiva were significantly higher at the maxilla than at the mandible. Four years after baseline, the implants in the mandible showed the smallest keratinized mucosa (mean: ≤ 1 mm). Conclusion: During the first 4 years after implant placement, no significant changes in the keratinized mucosa at implants could be shown, either in periodontally healthy patients or in patients treated for generalized aggressive periodontitis. The keratinized gingiva at the teeth was generally significantly wider than the keratinized mucosa at the implants. Keywords: aggressive periodontitis, dental implants, keratinized mucosa