137 small-for-gestational age (SGA) infants were examined in the neonatal period and at 2, 6 and 12 months. At each age a structured assessment was used for which a score denoting neurological maturation could be given. The SGA infants were significantly retarded compared with average-for-gestational age (AGA) infants from 2 months onwards. Within the SGA group the mean scores for boys, those who were first-born, breast-fed and/or born to mothers who smoked during pregnancy were in each case significantly higher than the rest at 6 and 12 months. Maternal smoking influenced all aspects of development at 12 months; whereas sex and method of infant feeding mainly affected the motor items, and birth order only those that were socially oriented. Positive associations were found between changes in somatic measures and changes in neurological scores from birth through to 6 months. Infants who grew faster also matured faster during this period of time, and vice versa. Positive correlations were found between size and scores at 2 and 6 months, but not at 12 months.