In an effort to understand factors underlying differences in the social organization of Pan troglodytes and P. paniscus, we measured the nearest neighbor distances and choices for chimpanzees in Kibale National Park, Uganda, and for bonobos in Lomako Forest, Zaire. We assume that the spatial organization of a set of individuals should reflect the underlying relationships between them. Bonobos were found to have smaller nearest neighbor distances than chimpanzees. The distribution and variability of the distances suggested that chimpanzees have a more restricted range of nearest neighbor distances than bonobos, avoiding situations of very close proximity. Selection of the sex of the nearest neighbor by a focal animal differed between the species. For example, male bonobos rarely had another male as their nearest neighbor, while male chimpanzees frequently did. Similarly, male bonobos tended to move apart when observed together, while it was female chimpanzees who tended to move apart when together. These observations are considered with respect to the nature of the social interactions in these species.