The aim of the present study was to estimate slow-wave activity (SWA), a marker of sleep homeostasis, in children with obstructive sleep apnoea (OSA) before and after adenotonsillectomy (AT) compared with untreated OSA children (comparison group). 14 children with OSA (mean ± sd age 6.4 ± 2.5 yrs; apnoea-hypopnoea index (AHI) 10.0 ± 10.3 events·h⁻¹) who underwent AT were consecutively recruited to the study. The comparison group comprised six retrospectively recruited children (age 5.4 ± 2.2 yrs; AHI 9.4 ± 7.6 events·h⁻¹) with OSA that did not undergo treatment. Electroencephalogram (derivation C3/A2) was analysed using spectral and waveform analysis to determine SWA energy and slow-wave slope. The same procedure was repeated 5.4 and 19 months later for the AT and comparison groups, respectively. AT improved respiration without a change in duration of sleep stages. Following AT, >50% elevation of SWA during the first two sleep cycles (p<0.01) and a more physiological decay of SWA across the night (p<0.0001) were noted. The slow-wave slope increased by >30% following AT (p<0.03). No significant changes were found in SWA in the comparison group. Sleep homeostasis is considerably impaired in pre-pubescent children with OSA. AT restores more physiological sleep homeostasis in children with OSA. SWA analysis may provide a useful addition to standard sleep-stage analyses in children with OSA.