Background: Individuals with Angelman syndrome appear strongly motivated by social contact, but there have been few studies that have examined the relationship between sociability and familiarity. In this study we compared social behaviour in Angelman syndrome when in contact with mothers and strangers. Methods: We systematically manipulated adult familiarity, eye contact and speech to examine the effect on social approach behaviours in children with Angelman syndrome. Eleven children (deletion 15q11-13) participated and were observed during interactions with their mother and an unfamiliar adult, while adult eye contact and talking were manipulated. Laughing and smiling, looking and social approach were observed. Results: There was no effect of familiarity on laughing and smiling or eye contact. Participants showed more social approach towards their mother than the unfamiliar adult but only when their mother was looking at them. Conclusions: In Angelman syndrome, looking at adults, laughing and smiling appear to be unaffected by the familiarity of the adult. However, approach behaviours are more common with mothers than strangers. The function of the approach behaviours might be to increase investment from the primary caregiver.