Aim To evaluate retrospectively the prevalence of vertical root fractures (VRFs) in a cohort of patients during apical surgery and the factors possibly associated with VRF. Methodology The sample consisted of 944 root filled teeth belonging to 768 patients (49.3% males and 50.7% females; mean age 43.5 ± 11.2 years, range 22–68 years), consecutively referred for endodontic surgery over a six‐year period. All patients underwent a clinical assessment of their signs and symptoms. Periapical radiographs of teeth that were candidates for endodontic surgery were taken. Sixty‐eight teeth with VRF were identified. Vertical root fractures were identified in pre‐surgical screenings in 32 cases (47.1%), and these did not undergo surgery. Another 36 cases of VRF were noted during the intervention for root‐end resection. The influence of posts, post type, tooth type, periodontal probing defects, spontaneous pain, sinus tract and follow‐up duration was assessed using a logistic regression analysis. Results Vertical root fractures occurred significantly more frequently (P < 0.001) when a post was present (61 VRF out of 377 teeth with post, prevalence 16.2%) than in teeth without a post (1.2%). Threaded posts and cast posts were significantly more involved in VRF than fibre, silica or carbide posts (P < 0.001). Most fractures (80.9%) occurred 1–5 years after root canal treatment. Sinus tracts, probing defects and spontaneous pain were significantly more associated with VRF cases than with nonfractured teeth. Conclusions In the present group of teeth, the major risk for VRF was represented by posts retained by actively engaging the canal via mechanical design (thread) or by frictional fit (cast).