BACKGROUND: Some spells consistent with TIA may be benign, such as those produced by migraine or migraine accompaniments in the elderly. Distinguishing these from embolic or thrombotic events may be difficult. METHODS: Emergency department physicians identified patients who presented with a presumed TIA at one of 16 hospitals in Northern California from March 1997 through February 1998. Recurrent TIAs and strokes were recorded for 90 days afterwards. RESULTS: Of 1,707 patients in whom TIA had been diagnosed in the emergency department, 191 (11.2%) had a recurrent TIA and 180 (10.5%) had a stroke during 90-day followup. Independent risk factors for recurrent TIA were age >60 years (odds ratio 1.9; 95% CI 1.2 to 2.9; p = 0.003), history of multiple TIAs (odds ratio 2.9; 2.1 to 4.0; p < 0.001), duration of spell =10 minutes (odds ratio 2.3; 1.6 to 3.3; p < 0.001), and sensory abnormality associated with the spell (odds ratio 1.9; 1.4 to 2.6; p < 0.001). Independent risk factors for stroke from a previous analysis were age, duration >10 minutes, diabetes, weakness, and speech impairment. Among the 30 patients with isolated sensory symptoms lasting =10 minutes, the risk of recurrent TIA was 40% and none had a stroke. CONCLUSIONS: In patients in whom TIA has been diagnosed in the emergency department, risk factors for subsequent stroke and recurrent TIA are different. A subset of patients with presumed TIA has a benign short-term course with multiple brief TIAs more frequently characterized by sensory symptoms.