Yamax SW-200 pedometer validity during unstructured free play was assessed in 13 preschool children aged 4.1+/-0.6 years using the Children's Activity Rating Scale (CARS). Pedometer validity and hip placement reliability were also assessed during straight line walking. Data were analysed using regression analyses, 95% upper and lower prediction intervals and 95% limits of agreement. The prediction intervals for pedometry were wide when using the CARS as a criterion. Limits of agreement and prediction intervals for directly observed step counts were also wide for pedometers, calling into question their acceptability for use with preschoolers. Limitations of employing the CARS direct observation approach as a criterion measure of physical activity are also discussed.