Background: Although preschoolers' physical activity in center-based childcare has received considerable attention, less is known regarding this group's activity levels within home-based childcare. This review aimed to explore and synthesize the literature on preschoolers' physical and sedentary activity levels in home-based childcare. Outdoor playtime was also examined to contribute to the understanding of preschoolers' activity levels within this particular setting. Methods: Nine online databases were searched for peer-reviewed, English-language, primary studies that quantitatively measured physical and sedentary activity levels of preschoolers attending home-based childcare. Studies were excluded if they were nonprimary research, if they lacked a preschool-aged sample, if they did not quantitatively measure physical or sedentary activity, or if they took place in an ineligible environment. Results: Seven articles were included in this review: 3 had objective measures of activity levels, and 4 relied on nonobjective measures. Accclerometry data suggest that preschoolers' average sedentary, moderate-to-vigorous, and total physical activity levels in home-based childcare ranged from 39.5 to 49.6, 1.8 to 9.7, and 10.4 to 33.8 min/hr, respectively. Outdoor playtime appears to be inconsistent in home-based childcare. Conclusion: Physical activity among preschoolers attending home-based childcare appears to be relatively low and widely varied. Sedentary time has received less attention in home-based childcare settings. Future research examining activity levels in this unique environment is warranted. (author abstract)