Hypoxic-ischemic brain injury is a very important neurological problem of the perinatal period and a major cause of chronic disability later in childhood. The subsequent neurological deficits are a variety of motor defects-especially spasticity but also choreoathetosis, dystonia and ataxia, often grouped together as "cerebral palsy," mental retardation, and seizures. The gestational age determines the neuropathology of the brain injury. One of the patterns of hypoxic-ischemic encephalopathy, typically affecting full-term infants, consists of parasagittal lesions and ulegyria. The aim of this study is to describe the magnetic resonance imaging (MRI) features and discuss the "suggested" pathogenetic mechanisms of this pattern, which affects the cortex and the white matter in a mainly parasagittal distribution; in this type of brain injury, the damage usually involves the deeper sulcal portion while sparing the apex, thus resulting in the so-called mushroom gyri characteristic ulegyric pattern. We discuss the MRI findings of parasagittal lesions and ulegyria in the brain examinations of 14 patients with a clinical history of perinatal hypoxia/anoxia presenting with mental retardation, seizures, and cerebral palsy. Differential diagnosis from polymicrogyria is discussed.