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Background: Recently, the Diffusion and Perfusion Imaging Evaluation for Understanding Stroke Evolution (DEFUSE) and the Echoplanar Imaging Thrombolytic Evaluation Trial (EPITHET) trialists suggested that diffusion-perfusion magnetic resonance imaging (MRI) can classify patients into 4 subgroups likely to differentially experience benefit or harm from reperfusion therapies. However, there is a lack of data comparing MR mismatch profiles between different race-ethnic groups. In addition, clinical factors affecting MR mismatch profiles are not well described. Methods: We analyzed clinical and pretreatment MRI data of patients from 2 geographically and ethnically distinct study populations (Seoul, South Korea, and Los Angeles, Calif., USA) who are eligible for recanalization therapy. Diffusion-perfusion mismatch regions were classified among the 4 DEFUSE MR profiles: target mismatch, no mismatch, small lesion and malignant. Results: A total of 147 South Korean and 162 Southern Californian subjects (64.2% Whites) were included. Pretreatment MRIs revealed that the MR mismatch profiles were different in the 2 study populations (p < 0.001). Target mismatch was more prevalent in Southern Californian subjects (67.9%) compared with South Korean subjects (58.5%), whereas the small lesion pattern was more prevalent in the latter (9.9 vs. 23.1%). After adjusting for covariables, 3 features independently decreased the likelihood of presence of target mismatch: history of diabetes (OR 0.369, 95% CI 0.196–0.694), small versus large arterial occlusion (OR 0.052, 95% CI 0.01–0.255) and largest size (highest tertile) of diffusion-weighted imaging (DWI) lesion volume (OR 0.516, 95% CI 0.266–0.999). The one feature independently increasing target mismatch likelihood was intermediate size (middle tertile) DWI volume (OR 2.977, 95% CI 1.431–6.195). Conclusions: Target mismatch profiles are present in 55–70% of patients. Target mismatch is less common in patients with diabetes, small vessel occlusion, Asian ethnicity and extensive DWI lesions, and more common in patients with DWI lesions of intermediate size. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]