Purpose <p>There is little available literature comparing paediatric periodic limb movement disorder (PLMD) and paediatric obstructive sleep apnoea syndrome (OSA). This retrospective study aimed to examine the impact of PLMD, OSA and OSA with an elevated periodic limb movement index (PLMI) on sleep quality and daytime symptoms.</p> Methods <p>This retrospective study examined 132 children who had been diagnosed with OSA (with or without elevated PLMI) and PLMD. All participants underwent overnight polysomnography. Patients were divided into three groups, patients with OSA with low PLMI, patients with OSA with elevated PLMI, and patients with PLMD. A comprehensive medical history was obtained for each participant, including comorbidities and sleep-related symptoms.</p> Results <p>Patients with PLMD were more likely to report prolonged sleep latency (<i>p</i> = 0.03). Children affected by both disorders were drowsier during the day (<i>p</i> = 0.04) and experienced more restless sleep (<i>p</i> &lt; 0.01). There was no difference in total sleep time (<i>p</i> = 0.97) or sleep latency (<i>p</i> = 0.26) between the three groups, but patients with PLMD had lower REM% (<i>p</i> &lt; 0.01), and children in the two OSA groups tended to have poorer sleep efficiency (<i>p</i> = 0.07).</p> Conclusions <p>In conclusion, sleep quality worsened due to both OSA and PLMD on their own. However, sleep quality did not worsen further when OSA with elevated PLMI occurred. Although no significant differences were observed in total sleep time or sleep latency, parents of children with OSA and elevated PLMI reported worse daytime sleepiness and restless sleep.</p>