Background: Evidence suggests that GABA may reduce pancreatic inflammation, protect β-cells from autoimmune destruction, and potentiate the regeneration of new β-cells in the setting of type 1 diabetes mellitus (T1DM). The enzyme GAD, also expressed in human pancreatic β-cells, is an antigenic target of reactive T cells. We hypothesized that treatment of children with recent onset T1DM with GABA or combination GABA with GAD will preserve β-cell function and ameliorate autoimmune dysregulation. Methods: This is a one-year, prospective, randomized, double-blind, placebo-controlled trial. Ninety-nine patients aged 4–18 years with newly diagnosed T1DM are randomized into three treatment groups: 1) oral GABA twice daily in addition to two injections of recombinant GAD enzyme, 2) oral GABA plus placebo GAD injections, or 3) placebo GABA and placebo GAD. Patients are evaluated at baseline and months 1, 5, 8 and 12. Mixed meal tolerance testing is performed at all but the 8-month visit. Laboratory studies will assess indices of beta and alpha cell function, glycemic control, immunophenotyping, and diabetes-related autoantibodies. Results: The primary outcome is the effect on pancreatic β-cell function as measured by meal-stimulated c-peptide secretion compared between the treatment groups before and after one year of treatment. Secondary outcomes include: 1) fasting and meal stimulated glucagon and proinsulin levels, 2) response in insulin usage by participants, 3) indices of immune cell function, and 4) effect on autoantibodies GAD65, ICA512, and ZnT8. Conclusions: This trial will determine the safety and efficacy of GABA and combination GABA/GAD therapy to delay T1DM progression in children.