Glioblastomas (GBM) are highly motile cancers that invade through normal brain. In the absence of curative chemotherapy this invasion, beyond surgical and radiotherapy margins, to distant brain sites is thought to be an important cause of treatment failure. Paradoxically, studies analyzing failure patterns have consistently shown that the large majority of failures occur at the original tumor site. This conflict may be explained by the fact these cancers are often only sub-totally resected and radiotherapy and chemotherapies fail to control this significant local cancer burden. We analyzed the failure pattern in 20 consecutive patients with complete resection of the gadolinium-enhancing portion of GBM demonstrated on the immediate post-operative magnetic resonance study, and who underwent a radical course of radiotherapy and chemotherapy. We found that recurrences occurred only at the resection margin in 17 of 20 patients. Recurrences were exclusively distant in 2 of 20 patients and occurred at both the resection margin and a distant site in 1 of 20 cases. We found that even in cases of complete resection of the gadolinium-enhancing portion of GBM 85 % of recurrences are localized to the resection margin.