Five patients operated on between 6 months and 7 years earlier for breast cancer were surgically treated for chronic subdural haematoma. This unusual association may be explained on the basis of known factors such as coagulative impairment subsequent to chemotherapy, a degree of cerebral atrophy or mild trauma. On the other hand, since four of the patients were taking antioestrogen therapy to control the disease, it is speculated that the oestrogenic properties of tamoxifen may have contributed to subdural bleeding.