Abstract Background Breast cancer and treatment can significantly affect bodily appearance. Older women are as likely as younger women to experience body dissatisfaction that is significantly related to poorer mental health. Despite this, the needs of older women for psychological support during cancer treatment remain under-studied. Aim This feasibility study investigated the efficacy and limitations of expressive writing as an intervention for body dissatisfaction following mastectomy for breast cancer. Methods 32 women who had mastectomy for breast cancer in the last 5 years were randomised to intervention (expressive writing) or control (factual writing) arms. Both arms completed 3×20-min writing sessions. The intervention arm wrote about their deepest feelings regarding surgery and the impact this had on how they feel about their body. The control arm wrote about their daily activities. Patients completed quality of life assessments 2 weeks and 3 months post intervention and attended an exit interview at 3 months. Results Analysis of the exit interviews showed that patients in the expressive writing group experienced a variety of benefits including; catharsis, reflection, expressing themselves anonymously and the facilitation of future discussions with friends, family and professionals. Negative experiences of the writing included; difficulties expressing emotions, ‘dredging up’ negative experiences and resistance to reflection. Conclusions Expressive writing is low-cost intervention that may benefit patients experiencing body dissatisfaction following mastectomy. Patients felt the intervention would be well received at the end of treatment and would be suitable to a broad range of patients who may not typically use support or therapeutic services.