Presently, prognosis of infants with perinatal hypoxia-ischaemia is estimated using the Sarnat scale, which combines clinical evaluation and electroencephalography, in combination with magnetic resonance imaging (MRI) and or evoked potentials. While the value of conventional MRI is limited during the first week of life, diffusion-weighted MRI demonstrates effects of acute cerebral ischaemia within hours of onset. However, the exact value of diffusion MRI in the prognosis of infants with hypoxia-ischaemia has to be established in larger follow-up studies. In this report we describe 5 term (post-conceptional age 40 1/7 to 41 2/7 week) neonates with severe hypoxia-ischaemia and a characteristic pattern of diffusion changes. T 1 -weighted images showed a hyperintense cortical signal in only one case and extensive hyperintensity in the basal nuclei in all 5 cases. T 2 -weighted images showed nearly complete loss of cortical delineation in three cases. Increased signal on diffusion-weighted images was seen throughout all cortical and subcortical areas while the cerebellum remained normal. This pattern, which we refer to as the "white cerebrum", is most readily apparent on coronal images. The apparent diffusion coefficient (ADC) was calculated and compared to that of four control infants. In the cortex ADC values were lowered (0.70 +/- 0.17 micro m 2/msec [mean +/- standard deviation (SD)]; controls [n = 4]: 1.18 +/- 0.02 micro m 2/msec) as compared to values of ADC in the cerebellum (1.31 +/- 0.06 micro m 2/msec [mean +/- SD]; controls [n = 4]: 1.25 +/- 0.06 micro m 2/msec). All infants died in the perinatal period. In summary, the "white cerebrum" on diffusion-weighted MRI indicates severe neonatal hypoxia-ischaemia and is the counterpart of the white cerebellum on CT.