Social excesses, characterised by heightened social motivation, are important for describing social functioning. Smith-Magenis syndrome (SMS) is a potential exemplar of a disorder where heightened social motivation is associated with negative behavioural outcomes. In Down syndrome (DS) strong social motivation is described, but less commonly associated with behavioural problems. Children with SMS (n = 21) and DS (n = 19) were observed during social situations, in which familiarity of adults present and level of attention available were manipulated. Motivation in SMS was characterised by comparatively frequent social initiations when adult attention was low, and stronger preference for familiar adults, compared to DS. Findings provide insight into the nature of social motivation in SMS and support an argument for nuanced consideration of motivation.