We have studied the role of systemic oxidative stress for survival of patients with head and neck squamous cell carcinomas (HNSCC). Patients with lowest plasma total GSH levels had the lowest 36 months survival. In patients with post-radiotherapy concentrations of plasma total GSH less than median value, about 73% died during the 36 months follow-up compared to about 21% of patients with GSH values above median. Systemic oxidative stress as assessed by low GSH in post-radiotherapy plasma is associated to outcome in HNSCC patients.