Peri-implantitis is a frequent finding in patients with dental implants. The present study compared two non-surgical mechanical debridement methods of peri-implantitis. Material and Methods Thirty-seven subjects (mean age 61.5; S.D +/- 12.4), with one implant each, demonstrating peri-implantitis were randomized, and those treated either with titanium hand-instruments or with an ultrasonic device were enrolled. Data were obtained before treatment, and at 1, 3, and 6 months. Parametric and non-parametric statistics were used. Results Thirty-one subjects completed the study. The mean bone loss at implants in both groups was 1.5 mm (SD +/- 1.2 mm). No group differences for plaque or gingival indices were found at any time point. Baseline and 6-month mean probing pocket depths (PPD) at implants were 5.1 and 4.9 mm (p=0.30) in both groups. Plaque scores at treated implants decreased from 73% to 53% (p < 0.01). Bleeding scores also decreased (p < 0.01), with no group differences. No differences in the total bacterial counts were found over time. Higher total bacterial counts were found immediately after treatment (p < 0.01) and at 1 week for ultrasonic-treated implants (p < 0.05). Conclusions No group differences were found in the treatment outcomes. While plaque and bleeding scores improved, no effects on PPD were identified.