Abstract Stress is an unavoidable condition in human life. Stressful events experienced during development, including in utero , have been suggested as one major pathophysiological mechanism for developing vulnerability towards neuropsychiatric and neurodevelopmental disorders in adulthood. One cardinal feature of such disorders is impaired cognitive ability, which may in part rely on abnormal structure and function of the hippocampus. In the hippocampus, the dentate gyrus is a site of continuous neurogenesis, a process that has been recently implicated in spatial pattern separation, a cognitive phenomenon that serves to reduce the degree of overlap in the incoming information to facilitate its storage with minimal interference. We previously reported that adult neurogenesis is altered by prenatal stress allowing us to hypothesize that prenatal stress may possibly lead to impairment in pattern separation. To test this hypothesis, both control (C) and prenatally stressed (PS) adult mice were tested for metric and contextual discrimination abilities. We report for the first time that prenatal stress impairs pattern separation process, a deficit that may underlie their cognitive alterations and that may result in defective behaviors reminiscent of psychiatric illness such as post‐traumatic stress disorder.Read less <