Classic magnetic resonance imaging (MRI) findings in patients with amyotrophic lateral sclerosis (ALS) are subtle, but some findings have been reported such as signal changes in the primary motor cortex and the corticospinal tract (CST). Only a few reports have discussed MRI findings of ALS with dementia (ALS-D), in which frontotemporal atrophy and hyperintensity in subcortical white matter of bilateral temporal tips have been reported. Recent development of diffusion tensor imaging (DTI) techniques allows us to extract specific white matter tracts and to analyze them quantitatively, i.e. we can visualize the CST and can also measure its integrity using DTI parameters such as fractional anisotropy (FA) or apparent diffusion coefficient (ADC). In patients with ALS, general decrease in FA and increase in ADC in the CST have been reported. In patients with ALS-D, several authors detected decrease in fractional anisotropy in the corpus callosum, the thalamus, frontal/parietal/temporal, the cingulate gyrus, and the uncinate fasciculus in addition to the CST. Voxel based morphometry or statistical analysis of imaging are the newly developed methods which enable to make objective and reliable imaging analysis based on automated procedure using standardized database. We also presented several researches using these techniques. In this article, we reviewed classic imaging findings and recent development of MRI including DTI and statistical imaging analysis in patients with ALS/ALS-D.