Prospective observations of 100 high-risk neonates by high-field (1.5 Tesla) magnetic resonance imaging of the central nervous system: I. Intraventricular and extracerebral lesions. The results of observations of the first 100 neonates at the University of Texas Health Science Center (Houston) who received magnetic resonance imaging of the central nervous system by means of a high-field image (1.5 T) are reported. All were assessed prospectively to be at risk neurodevelopmental delay. This first report specifically addresses the appearance of primarily hemorrhagic intracranial lesions, including intraventricular hemorrhage (n = 28), and extracerebral lesions, which include 3 cases of venous sinus thrombosis (n = 20). The signal intensities of hemorrhage underwent a characteristic evolution with time with only minor variations in the study group. Magnetic resonance imaging detected direct evidence of hemorrhage for up to 2 months, but hemosiderin was detected as a late indicator of hemorrhage for up to 9 months. Magnetic resonance imaging was equal in benefit to head ultrasonography and computed tomography for the diagnosis of intraventricular hemorrhage, but magnetic resonance imaging was also able to approximate the time of onset of hemorrhage. Magnetic resonance imaging was superior for the evaluation of extracerebral hemorrhage; ultrasonography failed to detect any of these lesions and computed tomography detected only 3 of 7. Short-term neurological abnormality was assessed, but the ability of magnetic resonance imaging to predict long-term neurodevelopmental delay is unknown and is the subject of an ongoing project. 