ObjectiveThis randomized controlled trial examines whether a briefer cognitive-behavioural (CBT) stress management intervention than the norm can reduce stress and distress and enhance benefit finding in women with breast cancer. It further aims to identify characteristics of those women most likely to benefit from the intervention.Design and methodA randomized controlled trial was conducted to assess the efficacy of a psychological intervention. Women (N=355) who had undergone surgery for breast cancer 4months earlier, the majority of whom were currently undergoing adjuvant therapy, completed questionnaires assessing global and cancer-specific stress, depression, anxiety, optimism and benefit finding. They were randomly assigned to a 5-week group cognitive-behavioural stress management (CBSM) programme plus standard care or standard care only. Reassessment occurred post-intervention and 12months later.ResultsAnalyses of variance revealed that patients who received the intervention showed significant lowering of global stress and anxiety and increased benefit finding compared to controls. These differences, however, were not maintained at 12months. Effects of the intervention were moderated by stress such that women with high global stress at baseline showed greater reduction in both stress and anxiety.ConclusionsA CBSM intervention, which was briefer than the norm (5weeks vs. 9-20weeks), had beneficial effects on adjustment for women with breast cancer and was particularly effective for those with increased global stress. Screening on this basis may facilitate optimal and cost-effective psychological treatment.Statement of contributionWhat is already known on this subject? Diverse psychological interventions have been utilized to enhance adjustment in women with breast cancer. Cognitive-behavioural therapy has been identified as the most promising intervention and has demonstrated short-term reductions in anxiety depression and quality of life. The findings from longitudinal studies are mixed, so more studies are needed which assess the durability of effects. Previous CBT interventions with women with breast cancer during the adjuvant treatment phase have ranged from 9 to 20weeks which is both time and resource intensive.What does this study add? This is a longitudinal randomized control trial with introduction of a CBT intervention conducted over a shorter period than previous interventions in the adjuvant treatment phase. The shorter intervention did enhance adjustment post-intervention, but differences were not sustained at 12months. In this study, positive and negative adjustments are assessed, and only two other CBT intervention studies have included positive outcomes. In this study, consecutive patients from a clinic are recruited versus selection through diverse methods as in other key studies of CBSM interventions. This is the only study to assess initial global stress as a moderator of the effects of a CBT intervention and women with high initial global stress did better in the intervention. A scale measuring this could be a useful screening tool to identify women in need of psychological intervention, thereby contributing to more cost-effective health care.