One hundred and fourteen consecutive patients with early breast cancer were entered into a study on the psychological effects of involvement in treatment choice. All women were offered counselling throughout. One group of women (n = 34), were advised to undergo mastectomy, due to the nature or position of the tumour. These women fared less well psychologically when compared on a battery of measures, before and after surgery, with women who were involved in choosing their own treatment (n = 80). The latter group itself was randomly allocated into two groups for taking explicit responsibility for treatment choice, using a double-blind procedure. These were a Patient Decision Group (n = 41) and a Surgeon Decision Group (n = 39). Results support the hypothesis that over and above the benefits of receiving their preferred treatment, women can further benefit from taking explicit responsibility for their treatment choice.