Most research focuses on preschoolers' primary non-parental child care arrangement despite evidence that multiple arrangements are relatively common. Using the nationally-representative Early Childhood Longitudinal Study, Birth Cohort, we compare characteristics and outcomes of families whose 4-year olds attend both home- and center-based child care with those who attend either home- or center-based care exclusively or receive no non-parental care at all. We find that about one fifth of 4-year olds attend both home- and center-based child care. Mothers' priorities for care (getting their child ready for school, matching their families' cultural background) and perceptions of good local care options predict their combining home- and center-based care. Preschoolers score higher on reading and math assessments, on average, when they attend centers, alone or in combination with home-based child care, than when they are cared for only in homes, either by their parents or by others. Preschoolers' average socioemotional outcomes generally do not differ between families who do and who do not combine care types. Implications for research and policy are discussed. (author abstract)