Persistent post-surgical pain is recognised as a major problem. Prevalence after different surgical procedures has been reported to range from 5% up to 85%. Limb amputation and thoracotomy have the highest reported prevalence. Prediction of persistent post-surgical pain has over the last decade caught attention. Several factors have been investigated, but in-depth knowledge is still scarce. The purpose of this study was to investigate the prevalence of persistent post-surgical pain, and predictive factors for persistent post-surgical pain 12 months after thoracotomy. A prospective longitudinal study was conducted. One-hundred and seventy patients were recruited before scheduled thoracotomy, and asked to answer a questionnaire. One-hundred and six patients completed the same questionnaire at 12-month follow-up. Regression analysis was performed to explore variables assumed predictive of persistent post-surgical pain. One-hundred and six patients (62%) filled out the questionnaire at both time points. Preoperative, 34% reported muscle-skeletal related chronic pain. At 12-month follow-up, 50% of the patients reported persistent post-surgical pain. Of the variables explored in the logistic regression model, only preoperative pain (P < 0.001) and dispositional optimism (P = 0.04) were statistically significant. In this study, preoperative pain was a predominant predictor for persistent postoperative pain (OR 6.97, CI 2.40-20.21), while dispositional optimism (OR 0.36, CI 0.14-0.96) seem to have protective properties. Our results show that preoperative pain is a predominant predictor of future pain. This implies that patients presenting with a chronic pain condition prior to surgery should be assessed thoroughly preoperatively and have an individually tailored analgesic regimen.