A young woman affected by multiple sclerosis (MS) was examined by magnetic resonance (MRI) during a relapse. Three months later the patient died from acute pulmonary embolism. An imaging and quantitative MRI study was performed on the formalin-fixed brain. Finally, the left hemisphere was examined by light microscopy after histological and immunocytochemical staining. While fixation significantly reduced T1 and T2 relaxation times, MRI signal and image contrast of the fixed brain were satisfactory. Lesion distribution was very similar in corresponding MRI slices and histological sections. The post mortem MRI scan and pathological study detected several new lesions, as expected from the patient's clinical course. Thus, it was possible to evaluate the age of lesions by comparing the MRI scans. In this study, signal intensity of MS lesions varied according to their histological features, i.e. to their age.