[en] To compare the detection rate of unenhanced CT, spin-echo T2-weighted, fast fluid-attenuated inversion-recovery(FLAIR), and diffusion-weighted MR imaging in the diagnosis of hyperacute middle cerebral artery(MCA) territory infarction. Sixteen patients with clinically proven hyperacute MCA territory infarction were evaluated with unenhanced CT and MR. All CT examinations were performed within six hours of the onset of symptoms and all MR studies were performed within two hours of CT. All images were evaluated independently by two radiologists in possession of brief clinical information. Positive imaging criteria were parenchymal hypoattenuation, as seen on CT, and increased signal intensity, as seen on MR. For quantitative analysis, we measured the attenuation and signal intensity of the lesion and contralateral normal parenchyma, and percentage contrast-to-noise ratios(CNRs) of the lesions were also calculated. Positive findings were detected in all patients on diffusion-weighted images, in 13(81%) on CT, in 10(63%) on fast FLAIR images, and in 7(44%) on T2-weighted images. Lesion percentage CNRs were 30% for diffusion-weighted imaging, 15% for CT, 18% for FLAIR MR imaging, and 16% for T2-weighted MR imaging(p < .004 for diffusion-weighted imaging vs others). For hyperacute MCA territory infarction, diffusion-weighted MR imaging was the most sensitive imaging technique and unenhanced CT was superior to fast FLAIR or T2-weighted imaging