Research Findings: Although there is a well-established relationship between economic stress and children's self-regulation, few studies have examined this relationship in children of Hispanic immigrants (COHIs), a rapidly growing population. In a sample of preschool children (N = 165), we examined whether economic stress predicted teacher evaluations of children's self-regulation, whether economic stress predicted children's physiological reactivity (via cortisol levels), and whether economic stress had a similar effect on self-regulation and children's cortisol for COHI versus nonimmigrant children. Greater economic stress was associated with poorer child self-regulation and heightened physiological reactivity across a challenging classroom task for the sample as a whole. However, when we examined children by group, greater economic stress was associated with poorer teacher-reported self-regulation for nonimmigrant children only. In contrast, greater economic stress was related to greater cortisol reactivity across a challenge task for COHIs but not for nonimmigrants. Practice or Policy: Results demonstrate the importance of considering physiological indices of self-regulation (heightened stress physiology), in addition to traditional external indices (teacher report), when assessing self-regulation or risk more generally among preschool samples that are diverse in terms of ethnicity, economic risk, and parents' nativity.