This study tested associations among parenting stress prior to a child's kindergarten entry, the sustainability of family routines, and biomarkers of stress among parents following the kindergarten transition. Parents (N = 51) with higher prekindergarten scores on the Parenting Stress Index Short Form reported lower Family Routines Inventory scores following school entry relative to their baseline. Declining family routines, in turn, were associated following kindergarten entry with greater 5-day mean and variance in evening cortisol, and higher C-reactive protein, an inflammatory mediator. However, only the cortisol findings remained significant controlling for baseline physiology. These findings support a family systems, social-ecological approach to life course development, wherein even mild challenges posed by children's normative transitions may reveal differences in parents' biobehavioral functioning. (Contains 3 tables and 1 figure.)