Leukodystrophies usually affect children, but in the last several decades, many instances of adult leukodystrophies have been reported in the medical literature. Because the clinical manifestation of these diseases can be nonspecific, MRI can help with establishing a diagnosis. A step-by-step approach to assist in the diagnosis of adult leukodystrophies is proposed in this article. The first step is to identify symmetric white matter involvement, which is more commonly observed in these patients. The next step is to fit the symmetric white matter involvement into one of the proposed patterns. However, a patient may present with more than one pattern of white matter involvement. Thus, the third step is to evaluate for five distinct characteristics-including enhancement, lesions with signal intensity similar to that of cerebrospinal fluid, susceptibility-weighted MRI signal intensity abnormalities, abnormal peaks at MR spectroscopy, and spinal cord involvement-to further narrow the differential diagnosis. ©RSNA, 2019.