BACKGROUND: There have been recent advances in the identification of people at high risk of psychosis and psychological treatments have shown promise for prevention. AIMS: To compare the longitudinal course of psychotic experiences and emotional dysfunction in high-risk participants receiving cognitive therapy with those receiving treatment as usual. METHOD: Data from a recent randomised controlled trial of cognitive therapy for people at risk of developing psychosis were utilised to examine three different statistical models that were based on 432 measurements of psychotic experiences and 421 of emotional dysfunction (anxiety-depression) contributed by 57 participants across the 13 measurement occasions (monthly monitoring for a year). RESULTS: Psychotic experiences and emotional dysfunction were correlated and decreased significantly over the course of the study, with most improvement in the early months. The reduction in positive symptoms, but not emotional dysfunction, was enhanced by allocation to cognitive therapy. CONCLUSIONS: Psychotic experiences and emotional dysfunction appear to interact in people at risk of developing psychosis. There appears to be a specific benefit of cognitive therapy.