Recent evidence has shown an association between diabetes mellitus and deficits in learning and memory. However, the mechanism by which cognitive abilities are impaired in diabetes has not been identified. The dentate gyrus of the hippocampus plays a significant role in spatial learning and memory. Studies in rodents show that learning tasks enhance neurogenesis in the dentate gyrus of the adult hippocampus. To investigate whether cognitive deficits in diabetes may be related to alterations in hippocampal neurogenesis, we measured the number of 5-bromo-2'-deoxyuridine (BrdU)-positive cells, an indicator of cell proliferation, in the dentate gyrus in an animal model of diabetes. Streptozotocin-induced diabetes produced a dramatic decrease in cell proliferation in the dentate gyrus as compared to controls. The results from this study suggest a potential role for alterations in neurogenesis in the cognitive decline observed in diabetes mellitus.