CT lung cancer screening is currently being implemented in clinical practice in the USA and pilot studies are ongoing in the UK.1 2 Recently, an European Union statement recommended planning the potential implementation of lung cancer screening in Europe.3 Overdiagnosis, the detection of a cancer through screening which would have never been diagnosed in the patient’s lifetime if screening had not occurred, is a harm that inevitably occurs with the implementation of a screening programme. Therefore, more information on the occurrence of non-aggressive disease is essential to aid in successfully implementing a screening programme that minimises overdiagnosis and overtreatment. Kale et al linked data from 1992 to 2010 of the Surveillance, Epidemiology, and End Results Database to Medicare claims in order to identify individuals with clinically detected, non-aggressive lung cancer in the USA.4 The authors find low rates of non-aggressive lung cancers in clinical practice, but advise caution, as the rate of non-aggressiveness among screen-detected cancers is ‘…likely to be different as screening with CT may unveil small, slowly progressive cancers that are biologically dissimilar’. However, non-aggressive clinically detected lung cancer may share characteristics with those of non-aggressive lung cancers detected by screening. Thus, information derived from non-aggressive lung cancers in clinical practice may aid in reducing overdiagnosis and overtreatment in lung cancer screening.