In amyotrophic lateral sclerosis (ALS), respiratory muscle weakness causes ventilatory insufficiency and tissue hypoxia, which induces a number of metabolic pathways, and in particular increases erythropoietin (EPO) synthesis. EPO is a glycoprotein with neuroprotective properties that stimulates erythropoiesis. Here, EPO plasma level in a large population of ALS patients, with and without respiratory failure, was measured. Plasma EPO level of patients with ALS (n = 98), controls with other neuromuscular diseases (n = 58) and healthy controls (n = 20) has been quantified by ELISA. No significant difference was found between ALS patients and the two control groups. EPO level was not different between bulbar- and spinal-onset patients and was not correlated with disease duration or functional impairment. However, in the ALS group EPO level was higher in females (p = 0.0006) and correlated positively with age (p = 0.006). The subgroup of ALS patients with respiratory failure had higher plasma levels of EPO compared with ALS patients with preserved respiratory function (p = 0.016), but short-term non-invasive ventilation did not change EPO level. In conclusion, EPO levels were found to be significantly higher in ALS patients with respiratory impairment representing preservation of this homeostatic mechanism.