Progressive loss of walking ability in amyotrophic lateral sclerosis (ALS) has been scarcely studied as a potential predictive factor for survival in motor neuron disease. We aimed to assess the progression of gait decline and its association with mortality in ALS using the Timed Up and Go test (TUG). Patients were followed up prospectively at the Centre for ALS and Related Disorders in Geneva University Hospitals between 2012 and 2016. The TUG was performed at baseline and subsequent evaluations occurred every 3 months. At inclusion, patients were classified as unable to perform the TUG, "slow TUG" (>10.6 s), and "fast TUG" (≤10.6 s). In total, 68 patients with ALS (mean ± SD age: 68.6 ± 11.9 years; 50% female) were included. Baseline TUG was negatively correlated with the total ALSFRS-R score (r = -0.63, p < 0.001). At baseline, ALS patients with bulbar onset performed the TUG faster (9.9 ± 3.7 s) than the non-bulbar ones (17.3 ± 14.9 s, p = 0.008). Thirty of 68 (44%) patients died by the end of the follow-up period. The TUG performance at the first visit did not predict mortality. While we did not find any association with mortality in ALS and gait quantification, the TUG was feasible in a majority of ALS patients, was correlated with functional status, and could be of interest in the follow-up of non-bulbar ALS patients.