Mothers and primary professional caregivers of 186 children, aged 6-30 months, participated in this study in which a new measure for daily stability in center day care was developed, describing staffing, grouping, and program features. Relative contributions of infants' daily experiences of care stability, quality of care, and mother's daily stress to the child's adjustment to day care were analyzed with hierarchical regressions. The child's adjustment was assessed with the Child Behavior Checklist (Achenbach, 1997) and with the Leiden Inventory for the Child's Well-being in Day Care. Children enrolled in fewer care arrangements showed less internalizing behavior and more well-being in the day care setting. Children had higher well-being scores when trusted caregivers were more available. Mother's family management stress was related to more internalizing problem behavior. Interactions between mother's daily stress and stability in care were found to affect the child's adjustment to day care.