In spite of emerging evidence of therapeutic benefit from non-invasive positive pressure ventilation (NPPV), only a minority of ALS patients use this therapy. We examined factors which correlate with use of NPPV in ALS patients. Data were analyzed from the ALS CARE Database on the use of NPPV in patients with FVC less than 50% of predicted and probable or definite ALS based on modified El Escorial criteria. Of the 403 eligible patients, 146 (36%) used NPPV. NPPV compliance was strongly correlated with symptoms of dyspnea and orthopnea as well as with the use of other therapies including PEG tubes, augmentative speech devices, and riluzole. Male gender and household income >$80,000 were also associated with higher NPPV use. There was no correlation between age, race, type of insurance, forced vital capacity, duration of symptoms, ALSFRS-R, caregiver burden or quality of life with the use of NPPV. These data suggest that the factors which are most closely associated with NPPV utilization are symptomatic orthopnea and dyspnea. The findings may be useful in designing prospective studies to examine the factors which might explain the underutilization of NPPV and the optimal use of this treatment.