Subcortical band heterotopia (SBH) or ‘double cortex’, is a congenital brain abnormality that results from aberrant migration of neurons during development of the cortex. MRI shows a continuous band of heterotopic grey matter located between the cortex and ventricular walls, separated from them by a thin layer of white matter. The condition is quite rare, found predominantly in females, and is occasionally familial with an X-linked dominant inheritance. Current research has focused on genetic and neurological correlates, with cognitive assessment restricted to a global measure of general intellectual functioning. This paper describes in detail the results of a neuropsychological assessment of a 9-year-old female recently diagnosed with SBH. Predominant features were a significantly reduced speed of processing for visuomotor and oral output and reduced immediate registration of information. This difficulty has functional implications affecting skill acquisition, learning in the classroom, and social interaction.