The prenatal period is a time of rapid development during which the fetus adapts to a wide range of experiences that may alter the infant’s developmental course. These experiences include exposure to conditions such as maternal stress, disease and the ingestion of a wide range of drugs. While great attention has focused, recently, on the effects of prenatal exposure to such drugs as cocaine and alcohol on newborn behavior, little is known about the effects of prenatal exposure to caffeine. Despite the widespread consumption of caffeine by mothers during pregnancy, recent investigations have suggested that caffeine may indeed function as a physical and behavioral teratogen. In addition to consistent findings of adverse physical outcomes such as prematurity and fetal growth retardation in both animals and humans, adverse effects of maternal caffeine consumption during pregnancy on behavioral development in the fetus have also been suggested by both comparative and human studies. For example, assessment of rodents prenatally exposed to caffeine generally show behavioral patterns of increased activity. Studies with humans using the Neonatal Behavioral Assessment Scale (NBAS) have shown that maternal caffeine consumption is related to differences in the ability of infants exposed to caffeine to regulate their level of arousal. The purpose of this study was to explore the relation between prenatal exposure to caffeine and newborn regulation of arousal, as measured by variations in neonatal heart rate and behavioral state. The heart rates and behavioral states of 50 healthy, full-term one to two-day-old neonates were assessed every 30 seconds for one hour between feedings. Measures of fetal growth and dysmorphology were also collected for each infant. Mothers were then interviewed about their caffeine consumption during pregnancy. When maternal nicotine and alcohol use during pregnancy were statistically controlled, results showed that infants who were prenatally exposed to higher amounts of caffeine had higher heart rates, both overall and during quiet and active sleep. In addition, these infants had experienced a higher number of obstetrical complications and were more likely to be from a lower socioeconomic background than infants prenatally exposed to smaller amounts of caffeine. These findings suggest that maternal caffeine consumption during pregnancy is related to altered levels of arousal among exposed infants. Since heart rate is an indicator of autonomic nervous system functioning, heavier maternal caffeine consumption during pregnancy may have subtle effects on nervous system (NS) development among exposed infants. These observed behavioral outcomes may, in turn, have long-term consequences for social and cognitive development.