Purpose: The purpose was to obtain normal values of the apparent diffusion coefficient (ADC) in the infant brain and to compare ADC maps with T1- and T2- weighted images. Method: Diffusion was measured in nine infants with an ECG-gated SE sequence compensated for first-order motion. One axial slice at the basal ganglia level was investigated with the diffusion- encoding gradients in the slice-selection direction. Results: On ADC maps, the corpus callosum and the optic radiations appeared dark before the onset of myelination, and the crus posterior of the internal capsule could be visualized before appeared on T1- or T2-weighted images. In gray and white matter, the mean ADC ranged from 0.95 x 10-9 to 1.76 x 10-9 m2/s. In the frontal and occipital white matter, in the genu corporis callosi, and in the lentiform nucleus, the ADC decreased with increasing age. The cortex/white matter ratio of the ADC increased with age and approached 1 at the age of 30 weeks. Conclusion: ADC maps add information to the T1 and T2 images about the size and course of unmyelinated as well as myelinated tracts in the immature brain.