Introduction: Triple A syndrome (AAAS) is a rare autosomal recessive disorder characterized by alacrima, achalasia, ACTH-resistant adrenal insufficiency, autonomic dysfunction, and progressive neurodegeneration. Increased oxidative stress, demonstrated in patients’ fibroblasts in vitro, may be a central disease mechanism. N-acetylcysteine protects renal function in patients with kidney injuries associated with increased oxidative stress and improves viability of AAAS-knockdown adrenal cells in vitro. Patient and Results: A boy diagnosed with AAAS presented with short stature and increased oxidative stress in vivo assessed by increased thiobarbituric acid reactive substances (TBARS), which are markers of lipid peroxidation, and by the susceptibility of LDL to oxidation and the capacity of HDL to prevent it. A homozygous missense germline mutation (c.523G>T, p.Val175Phe) in AAAS was identified. N-acetylcysteine (600 mg orally, twice daily) decreased oxidative stress but did not change the patient’s growth pattern. Conclusions: An increase in oxidative stress is reported for the first time in vivo in an AAAS patient. N-acetylcysteine was capable of decreasing TBARS levels, reducing the susceptibility of LDL to oxidation and improving the antioxidant role of HDL. The longterm effect of antioxidant treatment should be evaluated to determine the real benefit for the prevention of the degenerative process in AAAS.