Anatomists involved with studies of the hippocampal formation are being prodded by computational modelers and physiologists who demand detailed and quantitative information concerning hippocampal neurons and circuits. The beautiful camera lucida drawings of old, and the elegant descriptions of dendritic form that accompanied them are giving way to computer-reconstructed and three-dimensionally analyzed cells with rigorous determination of dendritic lengths and volumes, branching pattern and spine distribution. We will review certain quantitative aspects of hippocampal organization in the rat based on a survey of available literature and on our own intracellular labeling studies of granule cells of the dentate gyrus and pyramidal cells of the hippocampus. Some of the potential implications of these data for hippocampal information processing will be discussed.