ABSTRACT.We report the occurrence of a breach activity related to an osteolytic skull metastasis from an adenocarcinoma of the breast. A skull x-ray with retained electrodes identified the relationship of the focal high amplitude beta activity to a lytic lesion in the right parietal bone. Breach activity related to a skull bone metastasis has not been previously described, and has not to our knowledge been reported with lesions other than surgical and traumatic skull defects. The finding of an asymmetry in amplitude of the EEG activity in a patient with no antecedent history of head injury or neurosurgical intervention should raise suspicions of other skull bone defects which may result in a breach activity.