Aim: Night-time postural equipment (NTPE) can prevent hip subluxation in children with severe motor disorders (SMDs). However, it is unclear how it affects ventilatory function. The aims of the study were to determine how NTPE use affects ventilatory function and to compare night-to-night variability of ventilatory function in children with SMDs and typically developing healthy children. Method: Fifteen NTPE users (six males, nine females), aged 1 to 19 years (mean age 8y 7mo) alternated sleep condition between NTPE and sleeping unsupported for 14 nights. In all but two participants, gross motor function was classified as Gross Motor Function Classification System (GMFCS) level V; in the other two it was level IV. Oxyhaemoglobin saturation (SpO2) was monitored each night and transcutaneous CO2 (PtcCO2) for one night in each sleep condition. In 17 healthy children of similar age, home SpO2 only was monitored for seven nights. Results: In 13 of 15 NTPE users and 12 of the 17 typically developing children, SpO2 monitoring was satisfactorily completed. Of the children with SMDs, two had mean SpO2 levels below the treatment threshold for supplemental oxygen, which was uniquely associated with use of NTPE in only one participant, and three had nocturnal hypoventilation, which was uniquely associated with NTPE use in only one case. Night-to-night SpO2 variability was higher in children with SMDs than in typically developing children. Interpretation: NTPE may impair or enhance ventilatory function in a minority of children. Owing to night-to-night variability in SpO2, at least three nights of monitoring are recommended to determine optimal positioning for effective ventilation before and after NTPE introduction. This article is commented on by Lagerkvist on pages 686-687 of this issue. © 2013 Mac Keith Press.