Stroke refers to any damage to the brain or spinal cord caused by a vascular abnormality. This chapter shows how specific diagnostic information available from non-invasive investigations can be applied to the management of individual patients. The complexity of managing stroke patients is increasing. Early stroke classifications relied on clinical information. Terms such as 'transient ischemic attack (TIA)', 'minor stroke', 'reversible ischemic neurologic deficit (RIND)', 'stroke in progress' and 'completed stroke' were used to distinguish stroke subtypes. The initial diagnostic step should be to determine if the event is due to stroke or a non-vascular stroke mimic. The next level of stroke diagnosis is primarily to distinguish hemorrhagic from ischemic stroke. A detailed diagnosis of stroke etiology is required to plan management strategies for secondary stroke prevention. Stroke severity is an important diagnostic consideration in determining stroke prognosis, which in turn influences management decisions.