In the present study we investigated sleep hygiene and actigraphically evaluated sleep in 74 medication-naïve children, aged 6-12 years, with rigorously diagnosed attention-deficit/hyperactivity disorder (ADHD) and chronic sleep onset insomnia (ADHD-SOI) and 23 ADHD controls without insomnia (ADHD-noSOI). Between-group differences were analysed for lights out (sleep log), actigraphically evaluated sleep onset, sleep latency, total sleep duration, actual sleep time and sleep hygiene as measured with the Children's Sleep Hygiene Scale. We found a significant difference (P < 0.001) in mean (+/-SD) sleep onset between the ADHD-SOI group (21:49 +/- 0:56 h) and ADHD-noSOI groups (20:41 +/- 0:45 h). Sleep latency was significantly (P < 0.001) longer in ADHD-SOI (00:53 +/- 0:25 h) compared to ADHD-noSOI (00:26 +/- 0:25 h). The difference in total sleep duration between ADHD-SOI (9:42 +/- 0:44 h) and ADHD-noSOI (10:09 +/- 0:43 h) was not significantly different (P = 0.18). The group difference in actual sleep time was also not significant (8:43 +/- 0:52 h in ADHD-SOI versus 9:13 +/- 1:16 h; P = 0.40). There was no significant difference (P = 0.17) in mean (+/-SD) total sleep hygiene score between the ADHD-SOI (56.4 +/- 10.5) and ADHD-noSOI groups (53.0 +/- 10.6). We conclude that there were differences in sleep onset and sleep latency in ADHD children with chronic SOI and those without insomnia; however, sleep hygiene practices were similar and did not relate to sleep characteristics.