The present study examines the effect of dexamethasone treatment on the intensity of changes in T2-weighted and diffusion-weighted (DW) magnetic resonance images occurring in infant rats during and after cerebral hypoxia-ischemia. The right carotid artery was occluded under isoflurane anesthesia in 7-day-old rats and images were acquired in sedated animals using a Bruker 9.4 T magnetic resonance (MR) system. Imaging changes were markedly different in rats pretreated with dexamethasone phosphate (0.1 mg/kg, i.p.) 24 h before hypoxia than in controls. In control animals, areas of hyperintensity ipsilateral to the occlusion occurred during hypoxia-ischemia in both the DW- and T2-weighted images with some recovery of the changes in early posthypoxia. In contrast, in dexamethasone-treated animals, areas of increased hyperintensity in the MR images did not occur. Thus, dexamethasone treatment prevents MR imaging changes during ischemia, suggesting that the cytotoxic edema associated with energy depletion and/or ionic disturbances during ischemia are also prevented by dexamethasone treatment.