To classify the anatomic types of the right internal spermatic vein (ISV). We evaluated venograms obtained in 150 consecutive patients with idiopathic varicocele referred for transfemoral sclerotherapy. Six anatomic types of the right internal spermatic vein (ISV) were recognized. These were classified by the location of their orifices and the tributary venous patterns. In roughly half the patients (53%), the ISV appeared as a simple vein with no remarkable retroperitoneal interconnections. In the remainder, complex retroperitoneal anastomoses were encountered. By understanding these anatomic variations, the angiographer can approach treatment of right-sided varicocele with foreknowledge of the nature of these types and the presence of valves and collaterals.