We report of a large epidermoid tumor of the lateral ventricle in a 67-year-old man. Conventional imaging (CT, T1/T2, MRI) could not differentiate the tumor from the surrounding cerebral spinal fluid (CSF). On diffusion-weighted and diffusion anisotropy images the tumor was clearly seen as a hyperintense mass surrounded by hypointense CSF, highly suspected for epidermoid. Diffusion-tensor imaging (DTI) accentuated its lobulated structure and clearly demonstrated its relationship to neighboring white matter tracts. We suggest that in case of the suspicion of a space-occupying lesion in CSF containing areas, not distinguishable from CSF by conventional MR imaging, diffusion-weighted and diffusion-tensor MR imaging should be added.