In many fields of medicine, except seizure disorders, blood biomarkers have captured an integrated part of diagnostic decision making, including copeptin, the surrogate marker of vasopressin release. There are strong arguments to hypothesize circulating copeptin is elevated in epilepsy, especially in generalized seizures such as fever seizures (FS), and that copeptin is predictive for complexity and relapse at least in FS. Although long-term morbidity and mortality are both low in FS, there is high anxiety among parents because of a lack of criterions to identify children at risk for relapse. Copeptin may fill this gap by adding important diagnostic and prognostic information. Eventually, less children may receive needlessly over years fever drugs or anti-epileptic drugs.