Thoracotomy with rib spreading still remains the preferred approach for complex surgery. Rib fracture is considered a frequent involuntary event during this approach, but its real incidence has not been adequately investigated yet. In this study, we evaluated the incidence of rib fracture after thoracotomy, the possible risk factors and the relationship with post-operative pain and complications. We retrospectively analyzed the medical records of single-institution patients submitted to lateral thoracotomy from January 2016 to June 2023. Exclusion criteria were traumatic etiology and a medical history of osteoporosis. The presence of rib fracture was retrieved by surgical reports or post-operative chest X-ray. Basal and evoked pain after surgery was assessed by Visual Analogue Scale. The considered 30-day post-operative complications were atelectasis, need of endoscopic broncho-aspiration, pneumonia and pleural effusion. A total of 367 consecutive patients underwent thoracotomy in the study period. The median age was 68 (interquartile range 60-75) years. Rib fracture was detected in 179/367 (48.8%) patients. Incidence did not significantly vary throughout years (p = 0.98). The risk of developing post-thoracotomy rib fractures was significantly associated with age greater than the median value (p = 0.003). The presence of rib fracture was related to significantly more elevated evoked pain at 48h after surgery (p = 0.039) and a higher incidence of complications (32/179 vs 20/188; p = 0.047). Our study demonstrated that rib fracture occurs in almost half of the thoracotomies. Older patients are more likely to develop this event, which significantly correlates to increased evoked post-operative pain and higher rate of post-operative complications.