A system 100 and method for transcranial stimulation of a head region of a subject, comprises providing an electrode arrangement having a plurality of electrodes 104, 106 coupled to an electrode drive arrangement 102； in use the electrodes contacting the scalp of the head region 110 of the subject and the drive arrangement generating electrical signals for driving the plurality of electrodes to cause transcranial stimulation of the subject. A monitoring arrangement (202, Fig 2) is provided for monitoring spatial positions of the plurality of electrodes relative to the head region of the subject and/or mutual relative positions of the electrodes, and for indicating positional errors of the electrodes for enabling repositioning of the electrodes and/or a change in the electrical signals applied to the electrodes. A sensing arrangement may be provided to measure the spatial arrangement of the electrodes, for example an imaging sensor.
