Sixty consecutive patients admitted to a teaching hospital with acute stroke were studied prospectively for 3 months to define the natural history and consequences of lung aspiration. Using videofluoroscopy, aspiration was identified in 25 patients (42%) within 72 h of stroke onset, and had resolved in all but three patients (8%) after 3 months. It was closely related to the presence of dysphagia, which itself resolved within 2 weeks in all but the persistent aspirators. Lower respiratory tract infection (LRTI) was more common in aspirating patients (68%) than non-aspirators (6%). The use of intravenous fluids without oral intake did not appear to prevent LRTI in aspirating patients who were also dysphagic. Pneumonia occurred after 2 weeks in the three patients subsequently found to aspirate persistently. Aspiration is a transient phenomenon in most cases of acute stroke; it is associated with a high incidence of LRTI, but mortality in this series was not significantly associated either with respiratory tract infection or aspiration itself.