Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic disorder, characterized by hemosiderin deposition in the proximal renal tubules. We examined six cases of PNH with MRI including gradient echo imaging. On T2- and T2*-weighted imaging a characteristic hypointense pattern was noted in five of six patients with PNH. The extent of the hypointense area roughly correlated with the time elapsed from the latest hemolytic attack. T2*-weighted imaging (gradient echo imaging) is superior to T2-weighted imaging in the detection of hemosiderin in the renal cortex because of the higher sensitivity to magnetic susceptibility effect and shorter examination times. On the other hand, reversal of the normal cortical-to-medullary intensity ratio on T1-weighted imaging was not seen in our cases in which we used echo delay times short enough to neglect T2 effects.