Diagnostic difficulties in discriminating brain abscess from necrotic or cystic tumors using conventional CT and MRI have been reported. In this article, we examine the diagnostic ability of diffusion-weighted imaging to discriminate brain abscess from necrotic or cystic tumors. In previous reports, necrotic or cystic tumors show low signal intensity in diffusion-weighted imaging, indicating a high apparent diffusion coefficient (ADC). In contrast, in our study, high signal intensity was observed in the abscess fluid, associated with low ADC.