The behavior of 4 groups of infants--healthy term, healthy preterm, sick preterm, and sick full-term--was assessed in the neonatal period using the Neonatal Behavioral Assessment Scale (NBAS). At 3 months postterm, infants and their mothers were observed and videotaped in a free-play session. Both the NBAS and mother-infant interaction data were analyzed to assess the effects of maturity (term vs. preterm), illness (sick vs. healthy), and their interaction. Results revealed that illness of the infant affected both NBAS performance and maternal behavior during the interaction at 3 moths. Infants who were ill performed poorly on the NBAS orientation dimension; this dimension was found to be significantly associated with maternal and infant behaviors at 3 months. These data demonstrate an association between early infant characteristics and subsequent mother and child interactive behaviors. They also identify postnatal illness as an important influence on the development of the mother-infant dyad.