All patients with a definite ALS diagnosis, aged > 18 years, referred to the ALS outpatient clinics of the Fondazione Salvatore Maugeri Institute of Lumezzane (Brescia) and Istituto Don Gnocchi Onlus (Milano), Italy, for respiratory functional assessments for the purpose of early initiation of NIV were considered. Patients who were in clinically stable condition and without chest infections during the previous 3 months were considered eligible for the study.