A series of large amplitude potentials were recorded within and surrounding the hippocampal formation in association with repetitive, self-paced hand movements in the monkey. The earliest component precedes the onset of muscle contraction by approximately 100 ms, inverts in polarity across the pyramidal cell layer of CA3 and CA1 and is coincident with increased local multiple unit activity (MUA). Later components, generated within the hippocampal formation, follow the muscle contraction by as much as 600 ms and are not associated with net changes in MUA. The onset of voluntary movements is often associated with desynchronization of low-frequency rhythmic hippocampal EEG patterns and these changes antecede the movement. The findings strongly suggest that the hippocampal formation is involved in the initiation and control of even simple voluntary movements in the primate.