Disparities by socioeconomic status (SES) are seen for numerous mental and physical illnesses, and yet understanding of the pathways to health disparities is limited. We tested whether SES alters longitudinal trajectories of cortisol output and what types of psychosocial factors could account for these links. Fifty healthy children collected saliva samples (four times per day for 2 days) at 6-month intervals for 2 years. At baseline, families were interviewed about SES and psychosocial factors. Lower-SES children displayed greater 2-year increases in daily cortisol output compared with higher-SES children. These effects were partially mediated by children's perceptions of threat and by family chaos. These findings may help explain, and provide some first steps toward ameliorating, low-SES children's vulnerability to health problems later in life by identifying the tendency to perceive threat in ambiguous situations and experiences of chaos as factors that link low SES to 2-year hormonal trajectories.