Many reports of the occurrence of periventricular-intraventricular hemorrhage (PVH-IVH) are biased by the inclusion of both inborn and outborn infants. To obviate this selection bias we examined a large inborn population of low-birth-weight infants to determine if the incidence of PVH-IVH changed over a 3-year interval from March, 1982 through February, 1985. Serial cranial ultrasonography was performed in 463 consecutive infants of birth weight less than or equal to 1500 g who survived for more than 8 h. The incidence of PVH-IVH decreased from 31.5% and 29.3% in years 1 and 2, respectively, to 23.7% in year 3 (P less than 0.05). The latter reflected a fall in the incidence of grades III and IV PVH-IVH, but no change in the incidence of grades I and II. This observation was not attributable to changes in mortality, the distribution of infants by birth weight and estimated gestational age in each year of the study, or infants excluded from the analysis. Contrary to most reports, 21.9% of all PVH-IVH during the 3 years were first diagnosed after 14 days postnatal age and were predominantly grade I. These results document not only a change in the epidemiology of PVH-IVH in an inborn population, but also the importance of serial cranial ultrasonography beyond the first week of life.