This study explored the relationship between sensory processing abnormalities and repetitive behaviours in children with Williams Syndrome (WS; n = 21). This is a novel investigation bringing together two clinical phenomena for the first time in this neuro-developmental disorder. Parents completed the Sensory Profile (Short Form; Dunn in The sensory profile manual. San Antonio: The Psychological Corporation, 1999) and the Repetitive Behaviour Questionnaire (Turner 1995). A significant correlation was evident between the total scores on each of these measures; suggesting that children with WS who exhibit increased sensory processing abnormalities also display a higher number of repetitive behaviours. Further exploratory analyses of subscales of the measures indicated potentially important relationships that suggest a role for arousal regulation in the relationship between sensory processing abnormalities and repetitive behaviours in WS.