Objective: To evaluate the effect of patient- and tooth-related factors on the outcome of apical surgery in a multicenter study. Method and Materials: A total of 281 teeth in 255 patients undergoing periradicular surgery were investigated clinically and radiographically 6 to 12 months postoperatively. Results: The overall success rate was 88.0%. Sex was a significant (P = .024) predictor, with a success rate of 89.8% in females and 84.0% in males. The success rate was significantly higher in patients 31 to 40 years of age. The treatment of premolars resulted in a significantly higher success rate (91.9%) than the treatment of anterior teeth (86.1%, P = .042) and molars (86.4 %, P = .026). The loss of the buccal bone plate and the extension of apical osteolysis to the furcation area in molars resulted in a considerably lower success rate. Lesion size, preoperative pain, tenderness to percussion, fistula, and resurgery were significant factors. Conclusion: There are several factors influencing the success rate of apical surgery that must be taken into account when considering apical surgery as a treatment alternative. Keywords: clinical study, endodontic surgery, predictors, success rate