Recent findings suggest a relationship between early indicators of reactivity and later expression of inhibited temperament. The purpose of this study was to determine the relationship between neonatal medical and behavioral characteristics and behavioral inhibition at 18 months. The sample included 126 infants; 34 term (FT) and 92 preterm (<34 weeks gestational age and <1750g at birth), including 16 healthy preterm (HPT), 37 sick preterm (SPT), 18 preterm with Grade III or IV IVH (CNS), and 21 SGA. At one month (corrected), the Brazelton Scale was administered with simultaneous HR and the infant's cry was recorded and acoustically analyzed. At 18 months, infant behavior in response to a robot was videotaped. Behavioral inhibition was coded as approach and withdrawal behaviors to the robot. ANOVA results showed longer first contact (sec) in CNS and SGA, P<.05, longer latency to first withdrawal in CNS, P<.05, and longer latency to first contact in CNS and SPT, P<.05. Correlations between neonatal measures and 18 month inhibition scores showed higher Brazelton regulation related to more approaches (r =.23, P<.05) and higher HR on the Brazelton related to fewer approaches(r = -.23,P<.05). For cry, more energy was related to more approaches (r=.36, P<.01) and more withdrawals (r =.23, P<.05); more hyperphonation (high pitch) related to less exploration (r = -.23,P<.05); more dysphonation (dysregulated cry) related to less exploration (r = -.24, P<.05), fewer approaches (r = -.23,P<.05), and shorter latency to first withdrawal (r = -.24,P<.05). More variability in pitch was related to longer latency to first approach (r =.26, P<.05) and longer latency to first contact (r =.29, P<.01). Findings suggest effects of prematurity and medical complications on later expression of behavioral inhibition. In addition, neurobehavioral measures of neonatal dysregulation and increased reactivity predict more behavioral inhibition at 18 months.