Purpose: Implantoplasty, a procedure that is done to smooth contaminated implant surfaces, has been used in the treatment of peri-implantitis. It reduces the implant diameter, which might compromise the implant's strength. This in vitro study was designed to evaluate the effect of implantoplasty on implant strength. Materials and Methods: Thirty-two tapered implants were used; half were 3.75 mm in diameter (narrow) and the other half were 4.7 mm in diameter (wide). All implants were connected to 20-degree angled abutments. The apical half of each implant was embedded in acrylic resin. Eight 3.75-mm- and eight 4.7-mm-diameter implants were randomly assigned to receive implantoplasty. The remaining implants did not receive implantoplasty (control group). Implantoplasty was performed with a series of diamond and polishing burs. The specimens were then loaded 30 degrees off-axis in a universal testing machine until fracture failure occurred. Bending and fracture strength values were recorded and analyzed statistically (α = .05). The fractured surfaces were evaluated under a scanning electron microscope. Results: All narrow implants failed by fracture at the implant platform. The mean bending strength of narrow implants was statistically significantly reduced by implantoplasty (511.4 ± 55.9 N versus 613.9 ± 42.8 N). Implantoplasty did not affect the strength of wide implants; fracture failures occurred at the abutment screw. The fracture mode was ductile and the crack growth was oblique in direction, indicating complex stress distribution and concentration under loading. Conclusion: Within the limits of this study, implantoplasty appeared to weaken the strength of narrower implants. Therefore, this procedure should be performed with caution on narrower, freestanding implants that are subject to greater occlusal force (eg, posterior regions). Validation of these results is needed for different implant systems.