Diffusion-weighted imaging, dependent on motion of water molecules, provides information regarding tissue integrity. Apparent diffusion coefficient (ADC) values in the normal brain parenchyma, and those in a variety of lesions were studied by echo-planar diffusion MRI in 310 cases. Brain disorders were classified based on their ADC values, taking the ADC values of the normal brain white matter as the principal category. In the normal white matter ADC ranges were 0.60-1.05x10(-3)mm(2)/s, and the mean ADC value was 0.84+/-0.11x10(-3)mm(2)/s. It was possible to distribute brain disorders, as well as artefacts on diffusion MRI to five major categories: category 1, ADC similar to normal white matter; category 2, ADC lower than normal white matter; category 3, ADC higher than normal white matter; category 4, ADC similar to CSF; and category 5, markedly low or high ADC. Further studies can provide addition of different lesions as well as refinements of these categories.