The tissues placed on the edge of a glioblastoma's necrotic cavities are more vascularized than other pseudocystic central nervous system (CNS) tumours, both benign and malignant. The post-contrast enhancement is greater in Fluid-Attenuated Inversion-Recovery (FLAIR) images than in Spin Echo T1-weighted (SE T1w) sequences above all in the CNS tissues with a low concentration of gadolinium. The purpose of this study was to distinguish pseudocystic glioblastomas from other cystic CNS tumors by comparing post-contrast pseudocystic rim enhancement in FLAIR and SE T1-w magnetic resonance (MR) images. We investigated 32 extensive sets of MR images relating to histologically diagnosed pseudocystic CNS tumors; 14/32 were glioblastoma. Fast Spin Echo (FSE) T2-weighted and Proton Density, SE T1w and FSE FLAIR sequences were acquired in all the studies. After contrast media administration SE T1w and FLAIR sequences were acquired. In post-contrast T1w SE and T2w FLAIR acquisitions, pseudocyst rim enhancement was evaluated assigning scores: 4 = rim enhancement completely surrounds perimeter; 3 = rim enhancement in ≥50% of perimeter; 2 = rim in < 50% of perimeter; 1 = rim enhancement absent. Mean scores were calculated and the results were compared with statistical methods (Student's t test) for glioblastomas and all other tumors. Moreover differences between FLAIR and SE scores was assessed in each patient. If the difference was 0 glioblastoma was assumed, if the difference was ≥ 1 another tumor was assumed; the sensitivity and specificity of this diagnosis compared to the histological diagnosis were assessed. Mean T1-weighted SE scores did not differ in glioblastomas and other tumors. FLAIR scores in glioblastomas were less than half those of other tumors (p < 0.005). Glioblastoma diagnosis based on score difference identified 13 true positives (glioblastomas), 16 true negatives (non glioblastomas), two false positives and two false negatives. The sensitivity for glioblastoma was 86.7% and the specificity was 94.1%. Comparison of post-contrast rim enhancement in T1w SE and FLAIR sequences distinguishes glioblastomas from other pseudocystic CNS tumors, assisting the differential diagnosis of glioblastomas, that in many cases are not distinguishable from metastases even with advanced MR techniques.