A morphometric analysis of the human spiral ganglion was performed at an ultrastructural level. Cells of the basal, middle, and upper middle turns were evaluated by serial section. The following parameters were evaluated: myelinization, area, diameter, circumference, and degree of roundness of the cell body and nucleus; diameter of the axon and dendrite in their initial segments; and process configuration. Analysis of variance suggested there were at least two types of cell bodies within the human spiral ganglion, best delineated by the dimensions of the cell body and nucleus and the ratio of diameter of the initial segments of axonic and dendritic processes. Myelinization and degree of roundness were relatively unimportant differential parameters. Cluster (multivariate) analysis of the six most important differential parameters suggested the possibility of five subgroups among the groups of large and small cells. For the middle and upper middle turns, cluster analysis suggested that there may be as many as three groups of cells based on morphometric analysis. These results are discussed in relation to other morphologic and physiologic data in the mammalian spiral ganglion.