A best evidence topic in thoracic surgery was written according to a structured protocol. The question addressed was whether blood transfusion increases the chance of recurrence in patients undergoing surgery for lung cancer. Altogether 468 papers were found using the reported search, of which 21 represented the best evidence to answer the clinical question. The authors, journal date and country of publication, patient group studied, study type, relevant outcomes and results of these papers were tabulated. Nineteen cohort studies (two of which examined the same or similar data sets as two other studies already included), one comment article and one meta-analysis were identified. In total, the outcomes of 5378 patients undergoing surgical resection for lung cancer were analysed. The transfusion rate varied between 15 and 67%. The primary endpoints in all 21 papers were recurrence, survival or disease-free survival. We conclude that the research undertaken to examine the relationship between blood transfusion and lung cancer recurrence, survival and disease-free survival comes to no definite conclusion. Half of the papers relating to recurrence state that there is no significantly increased risk of recurrence with transfusion, whereas the other half state that there is. However, four of the five papers examining disease-free survival demonstrate a significant adverse relationship between this primary outcome and blood transfusion. With regard to survival, five of the papers reviewed showed no effect of blood transfusion, whereas five showed some form of adverse effect. Although there is no overwhelming agreement among the presented evidence, there is a slightly larger body of evidence supporting the theory that blood transfusions are associated with poorer outcomes in patients undergoing resection for lung cancer. However, whether this is a direct effect, or a surrogate marker for other factors such as anaemia, is unclear.