Diphyllobothrium latum infection in humans is not common in Republic of Korea. We report a case of fish tapeworm infection in a 10-year-old boy after ingestion of raw perch about 8 months ago. The patient complained of recurrent abdominal pain and watery diarrhea. A tapeworm, 85 cm in length, without scolex and neck, was spontaneously discharged in the feces of the patient. The patient was treated with 15-mg/kg single dose praziquantel, and follow-up stool examination was negative after one month. There was no evidence of relapse during the next six months.