The aim of our study was to determine whether fluid-attenuated inversion recovery (FLAIR) imaging and diffusion-weighted imaging (DWI) would be helpful in characterizing primitive neuroectodermal tumors (PNET) from other pediatric brain tumors. We expected that the compact cellular nature and the relatively small extracellular space of this tumor would affect the signal intensity on both pulse sequences relative to the more sparsely cellular glial tumors that have larger extracellular spaces. Eighteen pediatric patients with PNET were examined on a 1.5 T MRI with routine imaging plus FLAIR and compared with 28 patients with nonPNET. DWI was also performed in 7 PNET and 18 non-PNET. Seventyeight percent of PNET were isointense to gray matter on FLAIR while 82% of non-PNET were hyperintense and only one was isointense (3%). Diffusion was abnormally restricted in all 7 PNET examined (100%) but was restricted in non-PNET in only 1 out of 18 (6%) patients who had DWI. The differences in the histologic architecture between PNET and non-PNET are reflected in both FLAIR imaging and in DWI.