A brain arteriovenous malformation (AVM) is a tangle of abnormal vessels, the nidus, through which arteries drain directly into veins without a capillary bed. Most AVMs are sporadic, and multiple lesions suggest hereditary haemorrhagic telangiectasia (HHT). An AVM comes to attention through intracerebral haemorrhage or seizures, or as an incidental finding on imaging. Imaging defines its angioarchitecture, and the grade of the lesion frames the choice between observation, microsurgery, stereotactic radiosurgery (SRS) and embolisation, made by a multidisciplinary neurovascular team. The decisions that follow depend on whether the AVM has bled. The unruptured brain AVM page covers whether to treat an AVM that has not bled and how to follow it after radiosurgery. The ruptured brain AVM page covers the search for an AVM behind a haemorrhage, the timing of treatment and recovery.