This study was undertaken to identify findings on magnetic resonance (MR) imaging that might possibly differentiate among several dementia states in the elderly or predict response to shunt therapy in patients with normal-pressure hydrocephalus (NPH). The MR findings were retrospectively reviewed in 54 patients who were divided into four clinical categories: NPH (17 patients), obstructive hydrocephalus (eight patients), Alzheimer disease (eight patients), and non-Alzheimer dementia (21 patients). Three MR findings were evaluated in each case: increased periventricular (PVS) and white matter (WMS) signal on T2-weighted images, CSF flow void sign (CFVS) in the aqueduct, and corpus callosum thinning. Neither the PVS/WMS nor corpus callosum thinning patterns were useful for distinguishing among the four clinical groups. At low field strength, the absence of a marked or moderate CFVS, however, may militate against a diagnosis of NPH. All 17 patients with NPH underwent a shunt procedure after the MR study. A better response to shunt therapy occurred in patients without WMS and with more severe PVS.