['Atrial fibrillation (AF) is one of the most frequent complications occurring after thoracic surgery especially after lung resection. It is associated with an increase in postoperative morbidity and mortality. Recent data having documented the preventive role of corticosteroids on the occurrence of AF in cardiac surgery, we sought to evaluate the effect of preoperative administration of dexamethasone on the incidence of AF after pneumonectomy.', 'We reviewed the files of all consecutive patients who underwent a pneumonectomy in one single centre between July 2004 and July 2012. For each patient, demographics, medical status, the surgical procedure and treatments administered including dexamethasone, were recorded. The data were analysed using a univariate analysis and a multivariate logistic regression.', '153 patients were included and analysed; 35 (23%) presented with at least one episode of AF occurring within 48hours after surgery. Mortality was higher in these patients (26.5% versus 12.1%, p\xa0=\xa00.06) The univariate analysis indicated that patients who had a postoperative course complicated by the occurrence of AF were older (p\xa0=\xa00.003), had a higher SAPS2 score (p\xa0=\xa00.002) and a higher CHADS score (p\xa0=\xa00.05). Older age (OR\xa0=\xa01.08; p\xa0=\xa00.048) and pre-operative treatment by anti-arrhythmics (OR\xa0=\xa03.9; p\xa0=\xa00.029) were documented as independent risk factors in the multivariate analysis. Preoperative administration of dexamethasone 8\xa0-\xa012\xa0mg did not impair the incidence of AF.'] Is the risk of atrial fibrillation after pneumonectomy impaired by preoperative administration of dexamethasone . A cohort study?