We compared MRI and CT in a study of 175 patients; 87 infarcts within a week, 40 from 1 to 40 weeks, 25 a year after onset, and 23 hemorrhages, 18 within 2 weeks and 5 in 4 to 8 weeks. Fifty-nine infarcts and eight hemorrhages had sequential scanning. MRI is more sensitive than CT in the early detection of cerebral infarcts. CT is the method of choice to rule out intracerebral bleeding, but MRI is more specific in later stages of hemorrhage. Periventricular hyperintensity is seen more frequently with diabetes than without. Hyperintense white matter patches are often unrelated to clinical events. MRI is useful in following the evolution of strokes and distinguishing acute and chronic infarcts without contrast agents.