Prospective memory is a memory feature in humans which involves activities for remembering to do something in the future. The present study provides functional neuroanatomy of prospective memory for the first time. We used positron emission tomography (PET) and found several localized brain activations in relation to a prospective memory task required to retain and remember a planned action while performing an ongoing routine activity. Activations were identified in the right dorsolateral and ventrolateral prefrontal cortices, the left frontal pole and anterior cingulate gyrus, the left parahippocampal gyrus, and midline medial frontal lobe. We attributed these activations to several cognitive processes involved in prospective memory, such as holding an intention toward future behavior, checking target items within presented stimuli, and dividing attention between the planned action and the routine activity.