Pure monoparesis of the leg due to cerebral infarction is rare compared to that of the hand. The anterior cerebral artery (ACA) territory is the most common lesion site in leg monoparesis, but diffusion-weighted (DW) MRI has not commonly been used for lesion detection. The purpose of this study was to use DW MRI to evaluate the radiological correlation with lesion location in patients presenting with pure leg monoparesis. We retrospectively studied six cerebral infarct patients with pure leg monoparesis who had undergone DW MRI. Patients were scanned within 3 days of symptom onset. DW MRI identified lesions in the posterior limb of the internal capsule (PLIC) in two patients, in the corona radiata (two patients), in the subcortical white matter of the posterior frontal lobe (one patient), and in the frontal and parietal cortex, including the paracentral lobule and precuneus (one patient). The two patients with PLIC infarctions had characteristic linear infarction abnormalities along the long axis of the internal capsule. Corona radiata infarction were located posteriorly, and the two subcortical and cortical infarction were thought to be in the territory of the ACA. We thus concluded that in leg monoparesis due to infarctions, lesions may be located in the PLIC, corona radiata, or in the ACA territory. Recently, magnetic resonance tractography has shown that foot fibres of the corticospinal tract in the PLIC somatotopically may be posteromedial to hand fibres along the short axis of the internal capsule, rather than posterolateral along the long axis as has been thought. Thus, damage along the long axis of the PLIC by linear infarctions can cause pure monoparesis of the leg.