S P Liimatainen, J A Raitanen, A M Ylinen, et al. J Nerol Neurosurg Psychiatry, 2008; 79:808–12. The benefit of active drug trials is dependent on aetiology in refractory focal epilepsy. There is an error in the results section in the second paragraph: “The chances of achieving the remission were significantly higher in the patients with cryptogenic aetiology compared with symptomatic aetiologies (age-adjusted OR 3.74, 95% CI 1.54 to 9.07, p  =  0.04).” The correct p value should be 0.004, not 0.04.