We evaluated the impact of the severity of intrauterine growth retardation (IUGR) measured as the proportion of expected birth weight (birth weight x 100/median birth weight) on short-term neonatal complications and two-year infant neurodevelopmental outcome. The study was carried out on 236 singleton pregnancies complicated by idiopathic IUGR. The rates of bradycardia, respiratory distress syndrome, hypocalcemia, ventilatory support, apneic crises, transient neurologic signs and poor neonatal outcome (neonatal death or cerebral palsy) significantly correlated with the increasing severity of IUGR. In logistic regression analysis more severely growth retarded infants (< 67.5% of expected birth weight) had higher rates of bradycardia, respiratory distress syndrome, hypocalcemia and bacterial sepsis when compared with those less severely affected (84-67.5% of expected birth weight). In pregnancies complicated by idiopathic IUGR, most short-term neonatal complications are inversely related to the severity of growth failure as evaluated by the proportion of expected birth weight.