A representative sample (N = 120, 96%) of all pre-term (gestational age less than or equal to 36 weeks) infants born alive to mothers resident in the province of Kuopio, Finland, during a two year period, were studied at birth to evaluate the signs of intrauterine growth retardation (IUGR). Norms for somatic growth were based on measurements of birth weight, length and Ponderal Index (100 X birth weight (g) X birth length (cm)-3) of 51 pre-term singletons, born to healthy mothers after uncomplicated pregnancies, in relation to whom there were no discrepancies between menstrual dates and pediatric assessment of gestational age. The lower limits for normal ranges were defined as values two standard deviations below the expected means for the gestational age. Pre-term IUGR was diagnosed if birth weight and/or birth length and/or PI were more than 2 SD below the expected mean for gestational age. Different types of IUGR were found in 49 pre-term infants (41% of the pre-term population). A low PI was the most common descriptor of IUGR, being present in 42 out of 49 infants. A third of infants had more than one indicator of IUGR. In this population, pre-term IUGR was strongly associated with perinatal maternal pathology (especially hypertension, toxemia and prolonged leakage of amniotic fluid). The neonatal morbidity and mortality among pre-term IUGR infants was markedly higher than that among appropriately grown pre-term infants with corresponding gestational age. There were significantly more cases with fatal intraventricular hemorrhage in pre-term IUGR than in pre-term normally-grown infants.(ABSTRACT TRUNCATED AT 250 WORDS)