The purpose of this study was to describe nocturnal sleep and daytime nap duration in relation to salivary cortisol levels and child temperament in nonproblem nappers and problem nappers. Nighttime sleep and nap durations were obtained with continuous actigraph recordings for 3 days and nights (Tuesday, Wednesday, and Thursday) on 38 children aged 3 to 5 years who attended full-day child care centers. Nap times and disruptive behaviors were also observed and coded on each of the 3 days. Parents completed a temperament scale, sleep diaries, and the Children's Sleep Habits Questionnaire. Salivary cortisol samples were collected midmorning and in the afternoon after a nap on 2 consecutive days (Wednesday and Thursday). Problem napping and disruptive behaviors were associated with more negative affect, higher afternoon cortisol levels, and a smaller decrement in cortisol from morning to afternoon. Problem napping and disruptive behaviors were also associated with longer nighttime sleep, shorter nap durations, and later rise times. These data provide some insight into the associations among nighttime sleep, napping behavior, and salivary cortisol.