Full-term neonates from 37 pairs of same-sex twins, either small or appropriate for gestational age (SGA/AGA), were observed during the first sleep cycle after feeding to determine if behavioral indices of central nervous system (CNS) functioning were related to risk for the SGA infants. No differences were observed between groups for time spent in active or quiet sleep or length of the first sleep cycle. Both large and small limb movements were observed less frequently in SGA infants than AGA infants, and startles and spontaneous smiles were observed more frequently during active sleep in SGA infants than AGA infants. Consideration of behavioral state cycles as an index of CNS organization initially suggests that SGA neonates are not at higher risk than their AGA twins. Consideration of spontaneous behaviors during active sleep may be useful for early identification of individual SGA infants at risk. (Author/RH)