OBJECTIVE: To investigate self-assessment of the amyotrophic lateral sclerosis functional rating scale-revised (ALSFRS-R) using the patient's smartphone and to analyze non-inferiority to clinic assessment. METHODS: In an observational study, ALSFRS-R data being remotely collected on a mobile application (App-ALSFRS-R) were compared to ALSFRS-R captured during clinic visits (clinic-ALSFRS-R). ALS progression rate (ALSPR)-as calculated by the monthly decline of ALSFRS-R-and its intrasubject variability (ALSPR-ISV) between ratings were used to compare both cohorts. To investigate non-inferiority of App-ALSFRS-R data, a non-inferiority margin was determined. RESULTS: A total of 691 ALS patients using the ALS-App and 1895 patients with clinic assessments were included. Clinical characteristics for the App-ALSFRS-R and clinic-ALSFRS-R cohorts were as follows: Mean age 60.45 (SD 10.43) and 63.69 (SD 11.30) years ( CONCLUSIONS: Patients using a mobile application for remote digital self-assessment of the ALSFRS-R revealed younger age, earlier disease course, and faster ALS progression. The finding of non-inferiority of App-ALSFRS-R assessments underscores, that data collection using the ALS-App on the patient's smartphone can serve as additional source of ALSFRS-R in ALS research and clinical practice.