Identifying a stressor paradigm that elicits mean increases in salivary cortisol in young children has proven elusive, possibly due to characteristics of the paradigms used and how and when cortisol is sampled. We therefore examined the validity of a standardized task (adapted from Lewis and Ramsay, 2002) and procedures developed to assess cortisol reactivity in 215 preschool-aged children. Children participated in a standardized stress task during a home visit, which was videorecorded for future coding. Salivary cortisol samples were obtained at baseline and 10, 20, 30, 40, and 50 min post-stress. In support of the validity of the task, significant increases in cortisol levels from baseline were found, followed by a significant decline, and a quadratic function provided a good fit to the data. Children also showed a significant increase in negative emotions and a decrease in positive emotions over the course of the stress task. Results indicate that the task successfully elicited the hypothesized cortisol response in 3-year-old children.