An 8-year-old girl presented with defective motor coordination, a speech delay, behavioural problems, and generalised hypotonia. On examination, she was found to have hypermobile joints; a cardiac anomaly (patent ductus arteriosus); facial dysmorphism, and irregularly spaced, overcrowded teeth. Magnetic resonance imaging (MRI) of the brain performed as part of the neurologic work-up showed generalised hypodense white matter with multiple widely distributed foci of high signal intensity on the T2 and flair sequences . On T1 sequences, these areas were hypointense. Subsequent investigations confirmed an underlying rare chromosomal anomaly called tetrasomy X (48, XXXX). MRI changes associated with sex chromosome aneuploidies were extensively reviewed in a recent Australian publication. Although the exact relationship between the brain changes and neurobehavioural manifestations has not been elucidated, these changes are consistent with developmental aberrations, and could form the basis for the above manifestations in affected children.