Background: Psychological treatments have been shown to be effective in patients with psychosis. However, the studies published to date have included participants across wide age ranges, so few conclusions can be reached about the effectiveness of such treatments in relation to age. Aims: To evaluate outcomes by age in a randomised controlled trial designed to evaluate the effectiveness of cognitive-behavioural therapy (CBT), supportive counselling and treatment as usual. Method: Outcomes were evaluated in terms of symptoms, social functioning, insight and therapeutic alliance according to age at 3- and 18-month follow-up. Results: Younger participants responded better to supportive counselling than to treatment as usual and CBT over 3 months. Older participants responded better to CBT than to supportive counselling over 18 months. Younger participants showed a greater increase in insight after CBT compared with treatment as usual and supportive counselling, and were more difficult to engage in therapy. Conclusions: Young people may have different needs with regard to engagement in psychological treatments. Treatment providers need to take age-specific factors into account.