The present study assessed the association between habitual sleep patterns and one night of PSG measured sleep with daytime sleepiness in children with ADHD and typically developing children. Eighty-two children (26 ADHD, 56 typically developing children), between 7 and 11 years, had nighttime sleep recorded using actigraphy over five nights (habitual sleep patterns) and polysomnography during one night (immediate sleep patterns), both within their home environments. Daytime sleepiness was examined using the multiple sleep latency test within a controlled laboratory setting the following day. Using Spearman correlations, the relationships between mean sleep latencies on the multiple sleep latency test and scores on a modified Epworth Sleepiness Scale with polysomnographic measures of sleep quality and architecture and with actigraphic sleep quality measures were examined. Longer sleep latency, measured using polysomnography and actigraphy, was related to longer mean sleep latencies on the multiple sleep latency test in typically developing participants, whereas actigraphic measures of sleep restlessness (time awake and activity during the night), as well as time in slow-wave sleep, were positively related to mean sleep latency on the multiple sleep latency test in children with ADHD. These results show a differential relationship for children with ADHD and typically developing children between habitual and immediate sleep patterns with daytime sleepiness and suggest that problems initiating and maintaining sleep may be present both in nighttime and daytime sleep.