The development of 40 postterm, postmature infants was compared to that of 40 normal control infants during the first year of life. The postterm, postmature infants had more prenatal complications and received lower Brazelton interaction and motor scores at birth. At four months they scored lower on the Denver developmental scale and were rated "difficult" babies by their mothers. At eight months their Bayley motor scores were equivalent to those of the control infants, but their mental scores were lower. At this time their mothers reported a higher incidence of illnesses and of feeding and sleep disturbances.