Spinal cord infarction is a rare entity of varying etiology although most often associated with atherosclerotic aortic disease. Definitive diagnosis of (idiopathic) spinal cord infarction in the acute stage and in the absence of demonstrable predisposing factors is not always possible even with MRI. Diffusion-weighted MRI (dwMRI) may provide valuable information in the evaluation of spinal cord ischemia. A 45-year-old woman presented with idiopathic spinal cord infarction manifesting as sudden onset of paraparesis and sphincter dysfunction. Both T2-weighted and line-scan dwMRI revealed hyperintense signals in the dorsal part of the spinal conus. Apparent diffusion coefficient values were significantly low in the lesion, suggesting cytotoxic edema compatible with acute ischemia. The clinical course and other radiographic findings were also compatible with idiopathic spinal cord infarction. Diffusion-weighted MRI is an important diagnostic tool for examining patients with suspected spinal cord ischemia.