An implantable stimulation device is disclosed which provides for reduced power consumption when compared with bipolar stimulation and better stimulation performance when compared with monopolar stimulation. Implantable stimulator devices use less power in monopolar stimulation mode than that of bipolar stimulation but stimulation performance is greater when using bipolar stimulation. The device comprises circuitry capable of simultaneous stimulation between a reference electrode and an electrode of a stimulation array and between electrodes of the stimulation array, the ratio of current to the reference electrode and array electrodes being selectable.