Background: The application of cognitive therapy (CT) to psychosis is currently being developed in the UK. This paper reports a trial of CT in acute psychosis with the objective of hastening the resolution of positive symptoms and reducing residual symptoms.Method: Of 117 patients with acute non-affective psychosis, 69 satisfied inclusion criteria and 40 proceeded to stratified randomisation. The experimental intervention involving individual and group CT was compared with a group receiving matched hours of therapist input providing structured activities and informal support; routine pharmacotherapy was provided by clinicians blind to group allocation. Patients were monitored weekly using self-report and mental state assessments during admission and over the subsequent nine months.Results: Both groups showed a decline in positive symptoms but this was more marked in the CT group (P < 0.001). At 9 months 5% of the CT group, v. 56% of the control group, showed moderate or severe residual symptoms.Conclusion: CT appears to be a potent adjunct to pharmacotherapy and standard care for acute psychosis. Issues concerning internal and external validity of the study and opportunities for further research are discussed.