Aim: The purpose of the study was to assess whether postoperative periapical healing of apical periodontitis & postoperative pain differ in patients with controlled diabetes type 2 compared to diabetes-free patients  after receiving one-visit root canal treatment. Subjects and Methods: in a cohort prospective study, Forty six necrotic mature teeth with apical periodontitis of patients 18-60 years old were divided into 2 groups. A) Control group diabetic free patients B) Diabetic group who suffered from controlled diabetes mellitus type 2. Protaper files were used for mechanical preparation together with sodium hypochlorite irrigation and EDTA as a final flush. All procedures were done in single visit; follow-up was done up to 12 months using standardized digital radiographs. Results: preoperative swelling was significantly greater in diabetic group (P=0.047). Also, duration of session was significantly greater in diabetic group (p=0.016). In addition, there was a significantly greater postoperative pain incidence after 12 hours in diabetic group (P=0.027). While, no difference was found regarding postoperative healing at different follow up intervals in both groups. Conclusion: Generally necrotic teeth with periapical periodontitis were successfully treated regarding the healing of the periapical lesions. Single visit endodontic treatment of necrotic teeth with apical peridontitis, could be successfully done in controlled diabetic patients.