OBJECTIVE--To evaluate the effect of support from a nurse specialising in breast care and a voluntary support organisation on prevalence of psychological morbidity after surgery for breast cancer. DESIGN-- Prospective randomised study. SETTING--Three teaching hospitals in Glasgow with established breast clinics. SUBJECTS--272 women aged less than 70 years undergoing surgery for breast cancer. INTERVENTIONS-- Patients were randomly allocated to receive routine care from ward staff, routine care plus support from breast care nurse, routine care plus support from voluntary organisation, or routine care plus support from nurse and organisation. MAIN OUTCOME MEASURES--Prevalence of psychological morbidity as assessed by self rating scales: 28 item general health questionnaire and its subscales, and hospital anxiety and depression scale. Measurements were made at first postoperative clinic visit and at three, six, and 12 months after surgery. RESULTS-- On each self rating scale, psychological morbidity tended to fall over the 12 month period. For each scale, scores were consistently lower in patients offered support from breast care nurse alone compared with the other groups, which were similar to each other. Differences were significant or nearly so: P values were 0.015 (28 item general health questionnaire), 0.027 (anxiety and insomnia), 0.072 (severe depression), 0.053 (somatic symptoms), 0.031 (social dysfunction), 0.093 (hospital anxiety), and 0.003 (hospital depression). CONCLUSION-- Support from breast care nurse can significantly reduce psychological morbidity, as measured by self rating scales, in women undergoing breast cancer surgery.