OBJECTIVE: We set out to find a policy for the management of the pneumonectomy space which would minimise risk and be acceptable to all the surgeons. We believe this will reduce opportunities for error, be welcomed by nursing staff, and improve adherence to protocols. METHODS: We sought evidence in the scientific and educational literature. Finding no sure guidance, we audited our own experience of two policies, with the emphasis on minimising risk. RESULTS: There was no evidence from randomised trials. There was no cohesive advice in the text books. Our data indicated that it was improbable that randomised controlled trial (RCT) would have the power to find the evidence. Unable to establish the best strategy, we chose what appeared to be the lowest risk management policy. CONCLUSIONS: It is instructive that such a fundamental question should be unanswered. We have adopted a low risk and well established strategy--an unclamped underwater seal drain--but have no evidence base other than clinical experience. This is illustrative of much of what we do in clinical surgical practice. Avoiding major risk is often more important than proving small differences in benefit.