Background: Four expert panels from Australia, Canada, the United Kingdom, and the United States issued physical activity (PA) recommendations for young children that are quite similar. The aim of this study was to determine compliance with the new PA guideline (defined as [greater than or equal to] 15 min/hr of total PA) in two independent samples of preschool children. Methods: We conducted a cross-sectional study of children attending preschools in Columbia, South Carolina. A total of 286 children in one sample and 337 children in a second sample participated. The main outcome of interest was total PA (sum of light, moderate, and vigorous intensity activity) measured by accelerometry. Compliance with the PA guideline was determined for both samples. Separately for each sample, mixed logistic models were used to determine whether there were differences in compliance with the PA guideline between groups based on sex, race/ethnicity, parent education, and weight status, controlling for preschool. Results: Total PA was 14.5 and 15.2 min/hr in the first and second samples, respectively. The prevalence of meeting the PA guideline was 41.6% and 50.2% in the first and second samples, respectively. In both samples, more males than females met the guideline (53.5% vs. 33.5% and 57.6% vs. 45.9%) in the first and second samples, respectively (p 0.05). Conclusions: Approximately one half of children in two independent samples met the guideline for PA in young children. Policies and practices designed to increase PA among preschool children are needed, given that most children are not meeting this PA guideline. (author abstract)