Background: Abusive head trauma (AHT) in young children usually has a severe outcome when associated with hypoxic-ischemic encephalopathy (HIE), which is best characterized by MRI in the acute or subacute phase utilizing diffusion-weighted imaging (DWI). HIE in this setting has been hypothesized to result from stretching of the spinal cord, brainstem, or vasculature. Objective: To provide clinical correlation in patients with unilateral HIE and to postulate a mechanism in the setting of suspected AHT. Materials and methods: IRB approval was obtained. Over a 5-year period, the medical records and images were reviewed of the 53 children ≤3 years of age who presented with acute head trauma according to the hospital registry. The children were subselected in order to determine how many suffered either HIE or AHT, and to detect those with unilateral HIE. Results: In 11 of the 53 children, the etiology of the head trauma was highly suspicious for abuse. In 38 the head trauma was accidental and in 4 the trauma was of unknown etiology and at the time of this report was unresolved legally. Of the 53, 4 suffered HIE confirmed by CT or MRI. In three of these four with HIE the trauma was considered highly suspicious for AHT. Two of these three were the only patients with unilateral HIE, and both (7 months and 14 months of age) presented with early subacute phase HIE seen on DW MRI (range 4-7 days) and are described in detail with clinical correlation. The third child with AHT and HIE had bilateral findings. In the fourth patient the HIE was bilateral and was considered accidental. The work-up for both patients with unilateral HIE included head CT, craniocervical MRI, and craniocervical MR angiography (MRA). In both, there was mostly unilateral, deep white matter restricted diffusion, with subdural hematomas that were small compared to the extent of hypoxic-ischemic insult, and no skull fracture. Craniocervical MRA and axial thin-section fat-saturation images were negative for dissection, brainstem, or cord injury. Legal authorities obtained a confession of inflicted injury in one and a partial confession in the second (which did not fit the extent of injury). Five other children with HIE (based on DWI) were found during this period who had not suffered head trauma; all were bilateral insults. Conclusion: HIE associated with AHT might present with largely unilateral white matter injury on DWI following extensive cortical infarction. We propose that unilateral HIE in a young child might be a sign of AHT and might result from cervical vascular compression, whether from kinking during hyperflexion/ hyperextension or from direct strangulation. © 2007 Springer-Verlag.