Fragile X syndrome (FXS) is characterized by a constellation of cognitive strengths and weaknesses that differentiate this disorder from other forms of mental retardation. This unique cognitive phenotype emerges as the result of the silencing of the Fragile X Mental Retardation 1 (FMR1) gene. As a result, this syndrome provides an unprecedented opportunity to investigate the impact of a single gene on brain-behaviour relationships. This information is critical in elucidating the role FMR1 on normal neurological, perceptual, and cognitive functioning. Ongoing advances in this field provide emerging insights into potential pedagogical and therapeutic interventions to assist individuals affected by FXS. Here, we review current research on the neurological determinants underlying the perceptual and cognitive phenotype of FXS. A variety of methodologies have been used to explore these relationships. These include functional imaging, anatomical and behavioural studies of knock-out mice lacking expression of the fmr1 gene, neurobiological studies involving human and monkey brain tissue, and behavioural assessment of patients with FXS, focusing, on those studies that have established relationships between neurological abnormalities and specific perceptual/cognitive deficits. Finally, we will discuss the commonalities of the results from these multiple lines of research and conclude with an integrative account of this field with other known neurodevelopmental disorders.