The associations between deviant fetal growth and fetal to 1st year mortality were analysed using univariate and multivariate techniques in a very preterm birth cohort (N = 355; 285 live births; 70 stillbirths) born at or before 32 weeks' gestation in the province of Kuopio, Finland, in 1978-86. Regional fetal growth norms were obtained from non-malformed preterm singletons live-born during a separate five-year period to mothers without chronic diseases or pregnancy complications. Both small and large for gestational age preterms (SGAs and LGAs) showed significantly higher fetal to 1st year mortality (66% and 53%, respectively) than the appropriately-grown group (35%). However, the mortality risk increased markedly if deviant growth (either SGA or, in particular, LGA) was present in multiple fetuses. In such cases, careful follow-up of fetal and neonatal well-being is indicated through the remaining perinatal period. Interactions between perinatal variables should also be taken into account as determinants of outcome both in interventional studies and quality assessments of the care of mid-pregnancy fetuses and preterm infants.