Although rare, serious adverse effects may be seen after vaccination. Especially, the whole-cell pertussis vaccine has been held responsible for neurological side effects, as the most important problem in vaccination. With the advancement in vaccination technologies, whole-cell pertussis vaccine has been replaced by acellular pertussis vaccine, and neurological side effects have been significantly reduced. Herein, we present a 2-month-old male infant who suffered from generalized tonic-clonic seizures many times, possibly due to acellular pertussis after pentavalent vaccination, including diphtheria, acellular pertussis, tetanus, inactive polio, Haemophilus influenzae type B, and conjugate pneumococcal vaccine (BCG, DaBT-IPA-Hib, CPV).