This Clinic in Developmental Medicine describes a meticulous survey of germinal matrix/intraventricular hemorrhage in preterm infants, which took place in three New Jersey counties between 1984 and 1987. The babies under study weighed 501-2000g at their birth. They were studied prospectively with cranial ultrasound; the findings were correlated with very detailed pathological examination of the brains of those who died, and with later outcome in the survivors. The numbers studied in this population-based sample were large enough both to test and to generate hypotheses about the causes and consequences of hemorrhage.