Low socioeconomic status (SES) has been associated with higher levels of allostatic load (AL). Posited mechanisms for this association include stress, personality, psychosocial variables, coping, social networks, and health behaviors. This study examines whether these variables explain the SES-AL relationship in a population-based sample of 208 51- to 69-year-old White, Black, and Hispanic adults in the Chicago Health, Aging, and Social Relations Study. AL was based on nine markers of physiological dysregulation. SES was inversely associated with a composite measure of AL; hostility and poor sleep quality helped to explain the association between AL and SES. Factor analyses revealed four AL components corresponding to the bodily systems of interest. SES was significantly associated with two AL components, suggesting that the effects of SES on physiological dysregulation are specific to certain systems in a middle to early old-age population.