Background: Pneumonia after thoracic surgery considerably contributes to perioperative morbidity and mortality. So far, the forced expiratory volume in one second and diffusing capacity of the lungs for carbon dioxide are the most common validated prognosticators to estimate individual risk. Beyond functional parameters, modifiable risk factors for respiratory complications like pneumonia are poorly investigated in a prospective way. Thus, we aimed to assess the impact of oral health status in patients undergoing thoracic surgery and its correlation to perioperative outcomes. Methods: A prospective observational study included adult patients undergoing elective thoracic surgery from October 2, 2018 to April 29, 2020. The day before surgery, patients were examined by a dentist. Oral health status (caries, periodontal disease, tooth loss, and regular dental visits) was correlated with perioperative outcomes. Results: During the study period, 230 consecutive patients were included. Oral health status was poor in the study population. Postoperative complications were associated with active caries [odds ratio (OR) 2.5, P<0.03]. Patients with frequent dental visits and treated teeth had a lower risk for postoperative complications compared with patients without regular visits (OR 0.3, P<0.02). Patients with a high burden of caries had a significantly increased risk for pneumonia (OR 7.9, P<0.002). The forced expiratory volume in one second was a significant prognosticator for postoperative complications; however, no association between the forced expiratory volume in one second and oral health parameters was observed. Conclusions: A pathological oral health status is a modifiable factor predicting postoperative complications and pneumonia. A prospective randomized interventional study is warranted to clarify whether an improvement in oral health status can lead to a reduction of perioperative risk.