BACKGROUND There is a growing interest in using cognitive-behavioural therapy (CBT) with people who have Asperger syndrome and comorbid mental health problems. AIMS To examine whether modified group CBT for clinically significant anxiety in an Asperger syndrome population is feasible and likely to be efficacious. METHOD Using a randomised assessor-blind trial, 52 individuals with Asperger syndrome were randomised into a treatment arm or a waiting-list control arm. After 24 weeks, those in the waiting-list control arm received treatment, while those initially randomised to treatment were followed up for 24 weeks. RESULTS The conversion rate for this trial was high (1.6:1), while attrition was 13%. After 24 weeks, there was no significant difference between those randomised to the treatment arm compared with those randomised to the waiting-list control arm on the primary outcome measure, the Hamilton Rating Scale for Anxiety. CONCLUSIONS Trials of psychological therapies with this population are feasible. Larger definitive trials are now needed. DECLARATION OF INTEREST None. COPYRIGHT AND USAGE © The Royal College of Psychiatrists 2016. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence.