Objective: Deficiencies and excess of essential elements and toxic metals are implicated in amyotrophic lateral sclerosis (ALS), but the age when metal dysregulation appears remains unknown. This study aims to determine whether metal uptake is dysregulated during childhood in individuals eventually diagnosed with ALS. Methods: Laser ablation-inductively coupled plasma-mass spectrometry was used to obtain time series data of metal uptake using biomarkers in teeth from autopsies or dental extractions of ALS (n = 36) and control (n = 31) participants. Covariate data included sex, smoking, occupational exposures, and ALS family history. Case–control differences were identified in temporal profiles of metal uptake for individual metals using distributed lag models. Weighted quantile sum (WQS) regression was used for metals mixture analyses. Similar analyses were performed on an ALS mouse model to further verify the relevance of dysregulation of metals in ALS. Results: Metal levels were higher in cases than in controls: 1.49 times for chromium (1.11–1.82; at 15 years), 1.82 times for manganese (1.34–2.46; at birth), 1.65 times for nickel (1.22–2.01; at 8 years), 2.46 times for tin (1.65–3.30; at 2 years), and 2.46 times for zinc (1.49–3.67; at 6 years). Co-exposure to 11 elements indicated that childhood metal dysregulation was associated with ALS. The mixture contribution of metals to disease outcome was likewise apparent in tooth biomarkers of an ALS mouse model, and differences in metal distribution were evident in ALS mouse brains compared to brains from littermate controls. Interpretation: Overall, our study reveals direct evidence that altered metal uptake during specific early life time windows is associated with adult-onset ALS.