In order to incorporate patients ethically into randomised clinical trials, two related but distinct concepts are used: ‘Clinical Equipoise’ and the ‘Uncertainty Principle’. We argue that true ‘Clinical Equipoise’, a consensus of opinion regarding valid treatment options, is a more valid way of recruiting to neurosurgical randomised clinical trials than the ‘Uncertainty Principle’, which reflects an individual clinician's uncertainty. This subtle distinction has implications for both recruitment and interpretation of the results of randomised clinical trials.