BACKGROUND: The etiology of transient global amnesia (TGA) is uncertain. Recent studies have demonstrated a high signal intensity on diffusion MRI in TGA patients. In this study we reviewed and compared the use of electroencephalography (EEG) and diffusion-weighted imaging (DWI) in TGA in order to determine their sensitivity and to reveal clues about the etiology of this condition. METHODS: Twenty patients (7 males and 13 females; aged 58.0+/-12.1 years, mean+/-SD) who had been diagnosed with TGA at Dongguk University International Hospital within a 2-year period (2007 and 2008) were included in the study. All patients underwent EEG and DWI. RESULTS: The EEG of 12 of the 20 patients (60.0%) exhibited abnormalities; all 12 exhibited slowing on either the left side (n=6) or bilaterally (n=6). Spikes or sharp waves were detected in two patients. DWI revealed unilateral high signal intensities in the hippocampus of eight patients; five of these patients had left hippocampal lesions, and the other three had right hippocampal lesions. Four patients with a unilateral DWI lesion exhibited bilateral EEG abnormalities, and six patients exhibited only EEG abnormalities (without DWI abnormalities). Three patients had a high-signal-intensity lesion on DWI without EEG abnormalities. Five patients had normal EEG and DWI results. Interestingly, no patient had EEG abnormalities confined to the right temporal area. CONCLUSIONS: These findings suggest that left temporal dysfunction is important for the development of TGA. EEG might be complementary to DWI in TGA investigations, and may be superior at illustrating the associated memory dysfunction.