We examined the efficacy of cognitive behavioural therapy (CBT) delivered in groups on the reduction of symptoms of depression, anxiety and stress in young people on the autism spectrum. Utilising a quasi-experimental design, comparisons were made between individuals allocated to a group intervention program and individuals allocated to a waitlist. Following the intervention program, participants who were initially symptomatic reported significantly lower depression and stress scores on the Depression Anxiety Stress Scales in comparison to individuals on the waitlist. There was no significant change in anxiety related symptoms. The benefits were maintained at 3 and 9 month follow-up. Our findings demonstrate the potential of CBT in a small group setting for assisting young people with ASD who have symptoms of depression and stress.