The relationship between nursing care and the development of sleep-wake behaviors of 71 medically high-risk preterms was examined. The development of preterm infants' sleep-wake states, jitteriness, and negative facial expressions were influenced not only by the presence of the nurse, but also by the type of caregiving the nurse provided. The infant was awake more often when with caregivers than when alone. Waking states increased over time only when the infant was with caregivers, whereas quiet sleep increased only when the infant was alone. Infant behaviors and sleep-wake development were related to the intrusiveness of care. For example, negative facial expressions and sleep-wake transitions increased over time during the most intrusive caregiving. The development of sleeping and waking in preterm infants appears to depend not only on biological maturation but also nursing stimulation. As long-term developmental effects of nurse caregiving are unknown, additional research is needed.