This study reports group size, home range size, daily path lengths, seasonal effects on ranging behavior and qualitative information on diet for a population of hamadryas baboons inhabiting the lowlands of the northern Rift Valley in central Ethiopia. The minimum home range size and daily path length for this population are similar to those reported for other populations of hamadryas baboons in Ethiopia and Saudi Arabia. Group sizes, however, are much larger than those in most other hamadryas populations for which published data are available. The large group sizes in this area may be related to the abundance of one food resource in particular, doum palm nuts. Overall, this study suggests that hamadryas baboons may be more flexible in some aspects of their behavioral ecology (e.g. group size) than in others (e.g. ranging behavior).