Objective and practical biomarkers to determine the need for gastrostomy in patients with amyotrophic lateral sclerosis (ALS) are lacking. Tongue pressure (TP) is a promising biomarker because it is associated with bulbar dysfunction. The aims of this study were to evaluate the association of TP with the need for gastrostomy, and to determine its optimal cut-off value. This prospective observational study included participants with ALS taking nutrition orally. TP was evaluated using the Iowa Oral Performance Instrument. Need for gastrostomy as determined by a multidisciplinary team during a 12-month follow up period was recorded. Associations between TP and need for gastrostomy placement were performed. ROC curve analysis determined the optimal cut-off value of TP to predict gastrostomy. Of 208 screened participants, 119 were included. Gastrostomy was indicated in 45% (53), in a 12-month follow up period. TP of ≤20 kPA was a strong predictor of gastrostomy indication (OR 11.8, CI 95% [4.61, 34.7], p < .001). The association persisted even after adjustment for weight loss, pneumonia, prolonged feeding duration, Revised ALS Functional Rating Scale score, and American Speech-Language-Hearing Association scale score (OR 4.51, CI 95% [1.50, 14.9], p = .009). By receiver operating characteristic curve analysis, 20 kPA represented the optimal cut-off value (sensitivity 0.75, specificity 0.89). TP is a strong independent predictor of gastrostomy indication in the subsequent 12 months in patients with ALS, with good sensitivity and specificity at a cutoff value of ≤20 kPA, suggesting that it may be a promising biomarker in clinical practice.