Williams syndrome (WS) is a neurodevelopmental genetic disorder associated with 
high rates of anxiety and social issues. We examined diurnal cortisol, a 
biomarker of the stress response, in adults with WS in novel and familiar 
settings, and compared these profiles to typically developing (TD) adults. WS 
and TD participants had similar profiles in a familiar setting, while 
participants with WS had elevated cortisol late in the day in the novel setting 
when social demands were higher. The cortisol awakening response in WS was 
associated with parent-reported levels of somatic complaints and social 
difficulties. Results suggest that adults with WS have a typical diurnal 
cortisol profile that may be sensitive to social and activity transitions 
throughout the day.