Respiratory muscle involvement is one of the main prognostic factors in amyotrophic lateral sclerosis (ALS). Acute respiratory failure is sometimes the first manifestation of the disease, although onset can be more insidious. In the present retrospective study, it was proposed to review the clinical features and to assess the effects of non-invasive ventilation (NIV) on the prognosis of patients with respiratory onset, which was taken to be present when the first symptoms of muscular weakness were dyspnoea at exertion, dyspnoea at rest, or orthopnoea. Respiratory onset ALS is uncommon, since it accounts for less than 3% of ALS cases. ALS with respiratory onset has some common clinical features: male predominance, frequent camptocormia or dropped head, frequent widespread fasciculations, limb mobility fairly well preserved and significant weight loss in the early stages. ALS patients with respiratory onset still have a poor prognosis compared with those with bulbar or spinal forms. NIV should be proposed promptly because it improves the symptoms, general state of health and survival time. Efforts should be made to inform general practitioners and chest physicians and remind them that neuromuscular respiratory insufficiency may be attributable to this particular form of ALS.