Testicular germ cell tumors, though rare (1%), represent the most common neoplasm among young men. Gastrointestinal involvement from these malignancies usually presents as bowel obstruction and digestive bleeding, but their frequency is low (5%). The patterns of this involvement are: infiltration from affected retroperitoneal lymph nodes or, less frequently, by peritoneal seeding and direct hematogenous spread. Particularly, infiltration of duodenum is also rare, though its real frequency is not well defined. Moreover, the affinity for GI tract differs among the histological types of GCT, being seminomatous tumors an exceedingly unfrequent cause of duodenal infiltration. We herein present a recent case in our institution of severe anemia due to gastrointestinal bleeding in the context of giant retroperitoneal bulky metastatic mass infiltrating duodenum as first manifestation of a testicular pure seminoma.