There is a growing interest in understanding how the experience of socioeconomic status (SES) adversity across the life course may accumulate to negatively affect the functioning of biological regulatory systems important to functioning and health in later adulthood. The goal of the present analyses was to examine whether greater life course SES adversity experience would be associated with higher scores on a multi-system allostatic load (AL) index of physiological function in adulthood. Data for these analyses are from 1008 participants (92.2% White) from the Biomarker Substudy of the Study of Midlife in the US (MIDUS). Multiple indicators of SES adversity in childhood (parent educational attainment, welfare status, financial situation) and two points in adulthood (educational attainment, household income, difficulty paying bills, availability of money to meet basic needs, current financial situation) were used to construct SES adversity measures for each life course phase. An AL score was constructed using information on 24 biomarkers from 7 different physiological systems (sympathetic and parasympathetic nervous systems, hypothalamic-pituitary-adrenal axis, cardiovascular, lipid metabolism, glucose metabolism, inflammatory immune activity). Analyses indicate higher AL as a function of greater SES adversity at each phase of, and cumulatively across, the life course. Associations were only moderately attenuated when accounting for a wide array of health status, behavioral and psychosocial factors. Findings suggest that SES adversity experience may cumulate across the life course to have a negative impact on multiple biological systems in adulthood. An important aim of future research is the replication of current findings in this predominantly White sample in more ethnically diverse populations.