Purpose: Prolonged air leak (PAL) is a challenging complication in thoracic surgery. The aim of this study was to analyze the incidence, risk factors, and outcomes of PAL. Methods: We retrospectively analyzed 319 patients treated in a single center submitted to lobectomy, bilobectomy, segmentectomy, and wedge resections from January 2012 until August 2015. PAL was defined as air leak lasting more than 7 days after surgery. Results: The incidence of PAL was 14.7%. Bronchial obstruction (p < 0.05), low body mass index (BMI, p < 0.05), and hypoproteinemia (p < 0.001) were identified as independent preoperative risk factors of PAL. Intraoperative risk factors were lob- (p < 0.01) and bilobectomies (p < 0.05), pleural adhesions (p < 0.001), and length of stapler line (p < 0.001). Among the postoperative risk factors, we identified the use of active drainage (p < 0.01), the presence of subcutaneous emphysema (p < 0.001), massive air leak on the first postoperative day (POD 1, p < 0.001), and an incomplete re-expansion of the lung (p < 0.001). PAL was not associated with more complications in the postoperative period. One patient required reoperation due to a massive air leak. Twenty-six patients were discharged with a Heimlich valve with no complications and no need for re-admission. Conclusions: Bronchial obstruction, low BMI, hypoproteinemia, lob- and bilobectomies, pleural adhesions, length of stapler line, use of active drainage, the presence of subcutaneous emphysema, massive air leak on POD 1, and incomplete re-expansion of the lung were identified as independent risk factors of PAL. It had no influence on outcomes.