The study measured the prevalence and costs of complementary therapy use by women diagnosed with breast cancer in the South Thames NHS region. A postal questionnaire was sent to a sample of 1023 women from the Thames Cancer Registry who had been diagnosed with breast cancer in the previous 7 years. Just over a fifth (22.4%) had consulted a complementary practitioner in the previous 12 months. Almost one third (31.5%) had done so since diagnosis. Almost £17 000 had been spent on visits in the previous year. The women using complementary medicine after diagnosis were slightly younger, more educated and more likely to have used complementary medicine before their diagnosis than non-complementary medicine users. In conclusion, significant numbers of women are visiting complementary therapists for health reasons following a breast cancer diagnosis. The out of pocket costs per user, with notable exceptions, are modest. Use of practitioners of complementary therapies following diagnosis is a significant and possibly growing phenomenon.