PurposeStigma has been proposed to be one of the most serious obstacles to successful treatment, rehabilitation and inclusion in society of people with severe mental illness. An aspect of stigma which has been increasingly discussed is self-stigma, which refers to the internalization of negative stereotypes among people with severe mental illness. The aim of the present study was to investigate the effectiveness of a group-based anti self-stigma intervention, narrative enhancement and cognitive therapy (NECT) as an add-on to treatment as usual, with regard to changes in self-stigma, self-esteem, and subjective quality of life.MethodAfter screening for eligibility 106 participants were included in a randomized controlled trial using a wait-list control group, of which 87 completed the study. Assessments were made at baseline, at termination of the intervention, and at a 6-month follow-up (intervention group only).ResultsThe results showed that NECT was effective in reducing self-stigma and improving self-esteem compared to treatment as usual only. No differences were shown regarding subjective quality of life. Changes shown in the intervention group at termination of intervention were stable at the 6-month follow-up. A regression analysis showed that there was a positive relationship between exposure to the intervention and reduction of self-stigma.ConclusionsThe conclusion of the present study is that, using a sample size with adequate power, NECT seems to be an effective intervention with regard to diminishing self-stigma and improving self-esteem, and that these improvements were stable at a 6-month follow-up. There was a distinct relationship between number of sessions attended and improvements in self-stigma and self-esteem controlling for confounding factors. This puts attention to the importance of creating a group climate which facilitate and encourage participation through the various phases of the intervention.