Levetiracetam (LEV), used for both partial and generalized seizures, is a frequently preferred antiepileptic because of its few side effects. We present a 23-year-old man who developed hypokalemia after switching from valproate to LEV. The patient was sent to our clinic due to hypokalemia 1 month after initiation of LEV, and his neurological examination was normal. Further examinations revealed hypokalemia (3.1 mmol/L) and hypomagnesaemia (0.56 mmol/L). His hemogram, blood urea nitrogen, creatinine, total cortisol, thyroid function tests, creatinine clearance, and renal Doppler ultrasound were normal. LEV was tapered off and treatment with 200mg/day lamotrigine begun. Potassium and magnesium levels returned to normal ranges in subsequent tests. While hypokalemia and hypomagnesaemia have not been reported before to our knowledge, interstitial nephritis and renal failure after the use of LEV have been. Hypokalemia, found in the early period in this case, may be an indicator of a recently developed renal tubular disorder. This experience indicates that unpredictable side effects of increasingly used new antiepileptic drugs should be taken into consideration.