BACKGROUND Noninvasive mechanical ventilation is being used up to continuously by patients with Duchenne muscular dystrophy (DMD). Invasive and noninvasive tests are used to assess ventilatory function but there are few reports relating them to extent of ventilator dependence for which simple and cost effective parameters are needed. OBJECTIVE To investigate the relative efficacy of noninvasive lung function parameters for determining extent of need for ventilator use. MATERIALS AND METHODS 83 DMD patients were divided into three groups: no ventilator use (asymptomatic) (n = 26) [Group 1], nocturnal ventilator use (symptomatic) (n = 20) [Group 2], and full-time ventilator dependence (n = 37) [Group 3]. Tidal volume (TV), vital capacity (VC), respiratory rate (RR), inspiratory time (Ti), respiratory cycle time (Ttot), rapid shallow breathing index (RSBI [RR/TV]), breathing intolerance index (BITI), ventilator requirement index (VRI) and a new parameter RR/VC were monitored and compared. Data were analyzed with receiver-operating-characteristic curves (ROC) and the area under the curve (AUC) was calculated. RESULTS In group 2 and 3, patients used NIV for 3.3 ± 2.1 and 11.2 ± 4.7 years, respectively. By ROC comparison, RR/VC (RR/VC ≥ 0.024 [AUC, 0.921] and ≥0.071 [AUC, 0.935]), RR/TV (RR/TV ≥ 0.024 [AUC, 0.905] and ≥0.153 [AUC, 0.905]), and VC (VC ≤ 770 ml [AUC, 0.896] and ≤370 ml [AUC, 0.898]) represented to introduce nocturnal and continuous ventilator use, respectively. TV/VC, BITI, and VRI were either less sensitive or less specific. CONCLUSIONS Lung function parameters including RR/VC, RR/TV, and VC are useful and inexpensive in predicting the extent of need for ventilator use. Overall, RR/VC is the most appropriate predictor for determining extent of need for ventilator use.