A 47-year-old man presented with a 10-year history of left scrotal swelling. No solid mass detected on sonogram, dark-red colored fluid aspirated, equivocal cytology, and elevated serum CA19-9 level prompted surgical exploration. Frozen section reported no malignancy of thickening of the tunica vaginalis. The final pathology adenocarcinoma, however, necessitated left radical orchiectomy and hemiscrotal resection, demonstrating no malignancy at the left testis nor epididymis. CA19-9 level was high (104,200 U/ml) in the fluid obtained at the first surgery and the tumor cells were positively stained for CA19-9. Imaging study including abdominal CT scan and upper G-I series and normalization of CA19-9 level denied other tumor existing. In conclusion, this is to our knowledge the first case report of adenocarcinoma of the tunica vaginalis expressing CA19-9 antigen.