Summary:Numerous cases of atypical cerebral lateralization have appeared in the literature, yet these are heterogeneous and often fail to illuminate causal mechanisms. We evaluated neurobehavioral and neuroanatomical asymmetries in a 32-year-old woman with insulin-dependent diabetes mellitus, nonspecific immune dysfunction, and premature birth who developed Broca's aphasia, Gerstmann's syndrome, hemispatial neglect, and receptive paralinguistic impairments following a right frontoparietal infarction. She performed five out of seven tasks with her right hand, including writing. Using three-dimensional reconstructions of magnetic resonance images, we quantified the sizes of the left and right planum temporale (PT) and found her right PT to be larger than her left, a pattern associated with left-handedness. The presence of this structural asymmetry, which is known to develop prenatally, suggests that the factors responsible for this individual's anomalous neurobehavioral profile were present in the prenatal environment.