BACKGROUND the study of paraspinal muscles is pivotal for the diagnosis and staging of Amyotrophic Lateral Sclerosis (ALS), and is usually performed by electromyography. OBJECTIVE to evaluate the role of paraspinal muscle MRI as a diagnostic biomarker in ALS. METHODS we evaluated T1-w images of newly diagnosed ALS patients (n = 14), age-matched healthy controls (n = 11), patients affected by inflammatory myopathy (n = 10), and lumbar radiculopathy (n = 19), and compared them semiquantitatively by using the Mercuri Scale. RESULTS a significant difference in the appearance of the psoas muscle was observed between ALS patients and patients with radiculopathy (p = 0.003); after stratifying ALS patients into spinal and bulbar onsets, we found a significant difference in the appearance of the longissimus dorsi muscle between the spinal onset ALS subgroup and bulbar onset ALS subgroup (p = 0.0245), while no difference was found for multifidus (p = 0.1441), iliocostal (p = 0.0655), and psoas muscles (p = 0.0813) between the cohort subgroups. CONCLUSIONS paraspinal T1-w MRI could help to distinguish spinal ALS patients from healthy and pathological controls. Specifically, the study of longissimus dorsi could play the role of a diagnostic ALS biomarker.