The commonest context in which pulmonary metastasectomy is performed is for recurrent colorectal cancer. With a more active policy of surveillance among cancer teams, ready access to ever faster CT scans and a willingness to perform further surgery to control recurrent cancer, the practice of pulmonary metastasectomy is increasing. In this pro/con debate the issues are explored. It is recognized by both sides that there is no randomized trial evidence on which to base the practice. The difference of opinion is whether there is sufficient evidence from very many case series of both pulmonary and hepatic metastasectomy on which to base current practice. The surgeon's view is that the weight of evidence from many follow-up studies is in favour of continuing this practice. The mathematician's view is that case selection could account for nearly all the observed results.