The purpose of this study was to determine whether visual stimulation in sleeping infants and young children can be examined by functional magnetic resonance imaging. We studied 17 children, aged 3 d to 48 mo, and three healthy adults. Visual stimulation was performed with 8-Hz flickering light through the sleeping childs' closed eyelids. Functional magnetic resonance imaging was performed with a gradient echoplanar sequence in a l.5-T magnetic resonance scanner. Six subjects were excluded because of movement artifacts; the youngest infant showed no response. In 10 children, we could demonstrate areas of signal decrease during visual stimulation in the occipital cortex (mean decrease 2.21%), contrary to the signal increase observed in the adult controls (mean increase 2.82%). This decrease may be due to a higher proportional increase in oxygen extraction compared with increase in cerebral blood flow during activation. The different response patterns in young children and adults can reflect developmental or behavioral differences. Localization of the activation seemed to be age-dependent. In the older children and the adults, it encompassed the whole length of the calcarine sulcus, whereas it was restricted to the anterior and medial part of the calcarine sulcus in the younger infants. This may reflect a different functional organization of the young child's visual cortex or the on-going retinal development.