Background: Attention-seeking and impulsivity are reported to be problematic in Smith-Magenis syndrome (SMS) and have been linked to other challenging behaviours including self-injury and aggression. However, limited research has directly examined these aspects of the SMS behavioural phenotype. Method: A survey study refined descriptions of atypical social behaviour. Two further studies directly observed social behaviour, in both naturalistic settings and structured social situations manipulating familiarity of interacting adults and level of attention. A final study evaluated whether response inhibition, measured using cognitive assessments, underpins impulsive behaviour in SMS. Results: Caregivers reported elevated ‘attachment’ to particular people, but not generally elevated sociability. Natural observations revealed preferences for adult attention and manipulations of social variables indicated preference for familiar adults. Impulsivity was not associated with inhibition deficits, however emotional control was. Conclusions: Reports of atypical social behaviour were supported, characterised by seeking attention from familiar adults. Associations between impulsivity and emotional control implicate specific deficits in delay of gratification (whereby delay causes aversive emotional responses). Considering these findings in an integrated model of the SMS behavioural phenotype, including pathways from genetic difference to behaviour and environmental influences, may facilitate targeted interventions for challenging behaviours.