OBJECTIVE. Intraventricular hemorrhage in neonates with normally sized ventricles is overlooked when sonograms obtained via the anterior fontanelle fail to show a small amount of blood in the occipital horns of the lateral ventricle. Because visualization of the occipital horns is improved when sonograms are obtained via the posterior fontanelle, we studied the efficacy of posterior fontanelle sonography in establishing the diagnosis of intraventricular hemorrhage for 259 neonates. MATERIALS AND METHODS. We compared cranial sonograms obtained via both the anterior and the posterior fontanelles for 34 infants who had intraventricular hemorrhage and whose mean age at birth was 28 weeks (range, 23-40 weeks) with sonograms for 225 neonates who did not have hemorrhage and whose mean age at birth was 31 weeks (range, 24-42 weeks). Sonograms were assessed for satisfactory visualization of the occipital horns of the lateral ventricles, for the characteristics of intraventricular hemorrhage, if present, and for ventricular size, assessed as normal or showing mild, moderate, or marked dilatation. The technique of posterior fontanelle sonography involves obtaining parasagittal views of the occipital horns of the lateral ventricles and coronal scans of the occipital horns at the level of the calcarine fissure. The data from the contrasting groups of neonates were analyzed with Student's t-test or 2 x 2 tables as appropriate. Five autopsies were done; two confirmed intraventricular hemorrhage, and three confirmed the absence of intraventricular hemorrhage. RESULTS. Sonograms obtained via the posterior fontanelle were satisfactory for 92% of neonates born at less than 32 weeks' gestation and 88% of all neonates scanned. The mean age at birth of those with satisfactory sonograms obtained via the posterior fontanelle was 29 weeks (SD, 4 weeks); in comparison, a mean age at birth of 35 weeks (SD, 5 weeks) was associated with unsatisfactory sonograms (p < .0001). Intraventricular hemorrhage was detected via the posterior fontanelle but not via the anterior fontanelle on the initial diagnostic scan for 14 neonates. The ventricles were more likely to be normally sized when intraventricular hemorrhage was seen via the posterior fontanelle only (86%) than when intraventricular hemorrhage was seen via the anterior fontanelle as well (50%) (Fisher's exact test; p = .04). CONCLUSION. Our results show that sonograms obtained via the posterior fontanelle increase the rate of detection of intraventricular hemorrhage in neonates with normally sized ventricles.