ABSTRACT Rationale: Respiratory insufficiency is one of the most common causes of death in patients with neuromuscular disorders (NMD). Due to weakness and cognitive level, children with NMD often cannot perform required maneuvers to recruit lung volume. Data from cooperative adults suggest that breath stacking with a mask and one-way valve can obtain significantly higher lung volumes. Methods: To study the effectiveness of a breath stacking mask in patients with NMD, we studied 23 children (17 male, 6 female) over 3 years, mean age 11 y (range 3-19 y) and body mass 43.8 kg (range 12-80 kg). Fifteen were cognitively aware and able to communicate verbally. For involuntary breath stacking a one-way valve and pneumotach were attached to a cushioned mask that was held to the face, covering around nose and mouth with a tight seal. Flow signals were acquired to computer (AcqKnowledge BIOPAC Inc.). Tidal volumes (Vt) and minute ventilation (VE) were calculated from the recording for 30 s before and 30 s after 15 s of valve closure during which expiration was prevented. Oxygen saturation (SaO2) was measured. Results: The mean Vt before valve closure was 277 ml (range 29-598 ml). The mean increase in volume by stacking was 599 ± 558 ml (range -140 to 2,916 ml). When normalized to body mass, mean increase above normal end inspiratory level was 14.7 ± 14.7 ml/kg (range -2.7 to 52.2 ml/kg). The mean number of stacked breaths was 4.5 ± 3.6 (range 0-17). VE increased on average by 18% after stacking (p<0.05, paired t-test). There was no change in SaO2 after stacking. Four of the 23 children did not stack. Conclusions: Our findings show that breath stacking with a mask and a one-way valve can achieve breath volumes approximately 3x Vt. The mask was tolerated well, and cooperation of the child was not required.