Objectives The study aims to determine whether participation in structured group psychoeducation has an influence on the cognitive representation of illness and whether the basic personality traits are mediating factors in the process of its potential change. Method The study included 40 consecutive patients with the diagnosis of the bipolar disorder according to DSM IV who had an appointment at a surgery: the first 20 were included in the study group and the following 20 in the control group. All patients had to be in functional remission. The final statistical analysis includes 14 subjects from each group. The cognitive representation of the illness was presented in terms of the following variables: acceptance of illness, locus of health control, general self-efficacy, hope for success and beliefs about the condition. The intervention used was a structured group psychoeducation programme. Both groups were tested at three points in time (before intervention in the study group, after the intervention, and six months later). Results In the group who took part in the psychoeducation, statistically significant positive changes were observed in the internal locus of health control, the ability to find solutions, the sense of self-efficacy and the beliefs about the bipolar disorder during the tests directly after the end of the programme. Conscientiousness turned out to be a partial mediator for changes in terms of the ability to find solution. Conclusions Psychoeducation can have a positive effect on variables connected with cognitive representation of illness. Personality variables can have an influence too.