BackgroundCognitive difficulties are prevalent in people with a diagnosis of schizophrenia and are associated with poor long-term functioning.AimsTo evaluate the effectiveness of cognitive remediation therapy on cognitive difficulties experienced by people with schizophrenia.MethodParticipants with a diagnosis of schizophrenia, a social behaviour problem and a cognitive difficulty (n=85) were randomised to 40 sessions of cognitive remediation or treatment as usual in a single-blind randomised controlled trial. Working memory, cognitive flexibility and planning, were measured at weeks 0, 14 and 40.ResultsThere were durable improvements in working memory (advantage 1.33 points, 95% CI 0.43–2.16, standardised effect size 0.34) as well as an indication of improvement in cognitive flexibility. Memory improvement predicted improvement in social functioning. Costs were lower in the cognitive remediation group following therapy but rose at follow-up. However, cost-effectiveness analyses showed that improvements in memory were achieved at little additional cost.ConclusionsCognitive remediation therapy is associated with durable improvements in memory, which in turn are associated with social functioning improvements in people with severe mental illness.