Purpose: To evaluate postoperative pain after successful implant surgery and compare pain experienced using conventional flap and flapless techniques. Materials and Methods: Between January 2007 and September 2012, consecutive patients with bilateral partially edentulous maxillae or mandibles were included in the study. Patients were randomly allocated to receive implants with an atraumatic flapless procedure or with a conventional flap procedure in a split-mouth design in a two-stage surgery. This randomized blinded prospective clinical study considered each patient as one unit. The data were analyzed using the Mann-Whitney and chi-square tests. Results: One hundred eight implants were placed in 19 patients. Radiographic and clinical examination showed that all implants were successful. Postoperative pain was significantly more intense after surgery with the conventional flap technique than after surgery with the atraumatic flapless technique. Likewise, the inflammatory response was more intense with the flap technique. Conclusions: Postoperative pain depends on the surgical technique used and is less intense with a flapless technique.