Background Several studies have suggested a relationship between cognitive impairment and recidivism, but most have adopted a retrospective design. Aim The aim of this study was to test for any relationship between impaired executive function in adolescents with conduct disorder and subsequent recidivism up to 3 years later. Method In this prospective cohort study, 221 male adolescents with conduct disorder, admitted to a juvenile justice assessment centre for the first time, were interviewed about their offence, age, onset of delinquency and family history. They completed the Wisconsin Card Sorting Test (Keio version) (KWCST) and the Iowa gambling task. Scores were compared between those who subsequently re‐offended and those who did not. Results Seventy‐six (34%) participants re‐offended. There was no direct difference between groups in executive function, but there were age differences both in executive function and in recidivism. Multivariate logistic regression analysis indicated that the variables, which were independently associated with recidivism, were younger age, change in the person who brought up the child, and fewer (≤4) categories achieved on the KWCST. Recidivists were about twice as likely as single offenders to have achieved four categories or less on the KWCST (odds ratio 2.2, 95% confidence interval 1.1–4.4). Conclusions Impaired executive function appears to predispose to recidivism among young first‐time male offenders with conduct disorder. Our findings also suggest that further precise assessments of environmental stress on developing neurocognitive function could clarify the background of antisocial behaviour. © 2016 The Authors. Criminal Behaviour and Mental Health Published by John Wiley & Sons Ltd