Celiac disease (CD) is treated by eliminating all gluten from the diet. A 49-year-old man with CD was admitted to our clinic with complaints of recurrent diarrhea and abdominal pain despite strict adherence to a gluten-free diet. The duodenum was seen to be edematous on gastroduodenoscopic examination. Histological examination of the biopsy specimen taken from the duodenum showed multiple round shaped Strongyloides stercoralis (S. stercoralis) larvae within the crypts. He was successfully treated with albendazole. This case emphasizes the importance of duodenal biopsy in CD. To our knowledge, this is the first case in the literature showing CD and S. stercoralis together.