The value of biochemical tests in treating patients with uncontrolled seizures is unclear. We present the case of an 8-year-old boy with uncontrolled seizures receiving two antiepileptic drugs. He had been diagnosed with recurrent herpes encephalitis and treated with acyclovir 1 year previously. Laboratory blood analyses, performed because of his uncontrolled seizure episodes, revealed hypocalcemia. Hypoparathyroidism was detected with elevated levels of phosphorus and low levels of parathormone. In conclusion, blood tests, especially to measure calcium, in children with uncontrolled seizures are suggested. Hypoparathyroidism causing hypocalcemia, as present here, is not a rare occurrence.