Objectives. To see whether a cognitive behavioural guided self-help approach can reduce mental health symptoms, which patients might benefit most, and whether such a treatment increases self-efficacy and internal locus of control. Design. Repeated measures and correlational designs were used. Methods. 173 patients were recruited at a cognitive behavioural guided self-help clinic in Edinburgh, of which 97 completed the three-session intervention. Verbal IQ was estimated with the National Adult Reading Test (NART). Measures of emotional symptoms, self-efficacy and locus of control were taken before and after treatment, with follow-up at one month and six months. Results. Patients completing the intervention made favourable gains, which were maintained at six months. Self-efficacy and locus of control measures were not robustly correlated with mental health improvement, but did show pre- to posttreatment changes in themselves. Conclusions. Guided self-help appears to be a useful treatment option for those with depression, anxiety and stress. The implications of the findings, the strengths and limitations of the study, and areas for future research are discussed.