The links between sleep and attention-deficit hyperactivity disorder (ADHD) have been a topic for intense ongoing research and clinical interest. Previous narrative literature reviews conveyed a consensus that parents of children with ADHD are more likely to report sleep problems in their children in comparison to parents of control children. However, when objective measures are considered the results appear to be more complex and inconsistent. This review is based on a meta-analysis of relevant polysomnographic studies. We assessed measures related to sleep architecture, breathing disorders, and periodic limb movements in sleep (PLMS), and the role of potential moderators such as age, gender, and other methodological factors. The meta-analysis revealed only one significant combined effect that indicates that children with ADHD are more likely than controls to suffer from PLMS. Factors such as age, gender, inclusion of adaptation night, and comorbidity appear to play a moderating role in the associations between sleep characteristics and ADHD. To provide new insight regarding the links between sleep and ADHD research in this field should adopt new strict guidelines and consider the role of multiple pertinent moderating factors.