ABSTRACT Introduction There is a growing need for a robust clinical measure to assess upper limb motor function in spinal muscular atrophy (SMA), as the available scales lack sensitivity at the extremes of the clinical spectrum. We report the development of the Revised Upper Limb Module (RULM), an assessment specifically designed for upper limb function in SMA patients. Methods An international panel with specific neuromuscular expertise performed a thorough review of scales currently available to assess upper limb function in SMA. This review facilitated a revision of the existing upper limb function scales to make a more robust clinical scale. Results Multiple revisions of the scale included statistical analysis and captured clinically relevant changes to fulfill requirements by regulators and advocacy groups. Conclusions The resulting RULM scale shows good reliability and validity, making it a suitable tool to assess upper extremity function in the SMA population for multi‐center clinical research. Muscle Nerve 55: 869–874, 2017