Prior literature suggests that there may be relations between children's sleep disorders or inadequate amounts of sleep and behavioral adjustment. Most relevant studies concern clinical populations, however, and relatively few concern community populations. Moreover, previous studies have not addressed empirically the possible role of family functioning as a factor in the relation between children's sleep and adjustment. The present study, conducted in a predominantly low-income, community sample (N = 202), measured 4- to 5-year-old children's sleep patterns through daily logs kept by mothers, and measured family stress and parenting practices through detailed, multifaceted interviews and incidental observations of parent-child interactions. Children's adjustment, both positive and negative, was measured through preschool teacher reports on multiple occasions. A structural equation model showed that disrupted child sleep patterns (variability in reported amount of sleep, variability in bedtime, and lateness of bedtime) predicted less optimal adjustment in preschool, even after considering the roles of family stress and family management practices.