The authors present Japanese siblings of a 6-year-old girl and a 4-year-old boy, who concurrently experienced convulsions with mild gastroenteritis. These siblings, their father and paternal grandfather had afebrile seizures that intermittently occurred without symptoms of gastroenteritis and terminated within a few days at their infancy. An underlying genetic factor might not only cause benign familial infantile seizures but it might also confer the susceptibility to the convulsions with mild gastroenteritis in these siblings.