Although, classically, stroke symptoms are maximal at onset and patients gradually recover over days, weeks, and months, patients sometimes deteriorate. People have termed the phenomenon stroke progression, stroke in evolution, stroke deterioration, and symptom fluctuation. There is no consistent terminology. The phenomenon occurs from different causes and is incompletely understood. Although the typical definition of a significant neurological deterioration in trials has been a gain of ≥ 1 point on item 1a (level of consciousness) or ≥ 4 points in the motor items of the NIHSS, any detectable deterioration should prompt careful assessment and a tailored work-up.