The mother's voice, along with other developmentally appropriate sensory events (ie, touch, light, smells), stimulates maturation of the sensory systems and helps shape normal fetal development. While vast changes in the neonatal intensive care unit have occurred over the last 2 decades, little research has addressed the loss of exposure to maternal voice for the preterm infant. To address this gap, we compared studies that directly investigated effects of exposure to maternal voice on preterm infants. Studies reviewed were conducted between 1972 and 2007. All presented recordings of maternal voice at sound levels above current recommendations, and few of the findings reached statistical significance. Some potentially positive developmental effects were indicated. Future study of the effects of exposure to maternal voice on preterm infants using recommended sound levels is needed.