The aim of the present study was to determine the prevalence and frequency of stereotypy, self-injurious behaviour (SIB), and aggression in children and adults with Cri du Chat syndrome (CCS), and to investigate the relationship between SIB, aggressive behaviour and stereotypy in these individuals. Sixty-six families of children and adults diagnosed with CCS completed the Behaviour Problems Inventory. Additional information relating to gender, chronological age, type of school/post-school occupation and medication was also included in the survey. Stereotyped behaviour was reported for 82% of subjects, more than half the sample displaying it on a daily basis. The occurrence percentage of 15 topographies of SIB suggested that head banging, hitting the head against body parts, self-biting and rumination are the most frequently occurring behaviours in CCS. Aggressive behaviour was reported for 88%, with a statistically significant negative correlation between age and the number of aggressive behaviours reported. The present findings suggest that specific types of stereotypy and SIB are observed frequently in CCS.