Objective To evaluate the usefulness of diffusion-tensor MR imaging in brain white matter diseases. Methods A combined conventional and diffusion tensor MRI were obtained from 10 multiple sclerosis ,10 multiple lacunar infarction,3 cysticercosis,1 angiitis ,1 morphinist and 10 healthy control volunteers. After obtaining mean diffusivity (D) and fractional anisotropy images and image coregistration, the correlations of the lesions and the white matter pathways were investigated. D and AI values were measured form four big lesions which can be seen in T2WI and compared to contralateral white matter. Also D and AI value of four different anatomic locations of normal-appearing white matter regions were measured in all patients and controls. Results Whereas the lesions of infarction, cysticercosis and angiitis were in and outside the white matter pathways, all plaques of multiple sclerosis were inside the whit matter pathways. The brain white matter lesions by 1 morphinist were beside the lateral ventricle with big patchy appearance, which was partly inside white matter. For MS, D value was higher in lesions than control white matter. But for other diseases, D value could be seen higher or lower compared to healthy side. AI values were lower in all lesions. D value was higher and AI was lower in normal appearing brain white matter when comparing MS to other cases or healthy control volunteers. Conclusion Diffusion tensor MR images can determine the correlations of the lesions and brain white matter pathways. The changes of D and AI values can improve specificity in differential diagnoses though quantitatively analyzing the tissue damage in lesions and normal-appearing brain white matter.