CONTEXT: Pulmonary complications are the most common forms of postoperative morbidity in thoracic surgery, especially atelectasis and pneumonia. The first step in avoiding these complications during the postoperative period is to detect the patients that may develop them. OBJECTIVE: To identify risk variables leading to early postoperative pulmonary complications in thoracic surgery. DESIGN: Prospective study. SETTING: Hospital das Clínicas, Faculdade de Ciências Médicas, Universidade Estadual de Campinas. PATIENTS: 145 patients submitted to elective surgery were classified as low, moderate and high risk for postoperative pulmonary complications using a risk assessment scale. PROCEDURES: The patients were followed up for 72 hours after the operation. Postoperative pulmonary complications were defined as atelectasis, pneumonia, tracheobronchitis, wheezing, prolonged intubation and/or prolonged mechanical ventilation. MAIN MEASUREMENTS: Univariate analysis was applied in order to study these independent variables: age, nutritional status, body mass index, respiratory disease, smoking habit, spirometry and surgery duration. Multivariate logistic regression analysis was performed in order to evaluate the relationship between independent and dependent variables. RESULTS: The incidence of postoperative complications was 18.6%. Multivariate logistic regression analysis showed that the variables increasing the chances of postoperative pulmonary complications were wheezing (odds ratio, OR = 6.2), body mass index (OR = 1.15), smoking (OR = 1.04) and surgery duration (OR = 1.007). CONCLUSION: Wheezing, body mass index, smoking and surgery duration increase the chances of postoperative pulmonary complications in thoracic surgery