Objective: The objective of this study was to compare caffeine consumption in the morning, afternoon, and evening in adolescents with and without ADHD and examine associations with sleep functioning. Methods: Participants were 302 adolescents (ages 12-14) with (n=140) and without (n=162) ADHD. Adolescents wore actigraph watches to assess total sleep time and wake after sleep onset and reported on sleep-wake problems and the number of caffeinated beverages consumed per day in the morning, afternoon, and evening. Parents reported on adolescents' difficulties initiating and maintaining sleep. Chi-square analyses, odds ratios, and path analyses were conducted. Results: Analyses controlled for sex, medication status, and pubertal development. Adolescents with ADHD were 2.47 times more likely to consume caffeine in the afternoon and evening than adolescents without ADHD. Path analyses indicated significant associations between afternoon caffeine use and more self-reported sleep problems for adolescents with and without ADHD, and an association between evening caffeine use and self-reported sleep problems only in adolescents with ADHD. Afternoon caffeine use was associated with parent-reported sleep problems in adolescents with ADHD but not in adolescents without ADHD. Caffeine use was not associated with actigraphy-assessed sleep. Conclusions: This is the first study to show that adolescents with ADHD consume more caffeine than peers during later times of the day. Additionally, caffeine use is more consistently associated with poorer subjective sleep functioning in adolescents with ADHD compared to adolescents without ADHD. Pediatricians and mental health professionals should assess for caffeine use in adolescents with ADHD and co-occurring sleep problems. [This paper was published in "Journal of Pediatric Psychology" v45 n6 p643-653 2020.]