The aim of this study was to quantify the anatomic and hemodynamic components of the testicular venous drainage for the purpose of understanding their mechanisms of interacting in producing mutual effects, such as "nutcracker" phenomenon, reflux, and varicoceles. Seventy-five male subjects were studied at rest and during Valsalva maneuver. Aortomesenteric distance and angle, flow velocity in different segments of the renal veins, testicular vein diameter, and flow inversion were evaluated using standard ultrasound equipment with spectral and color Doppler capabilities. The velocity of flow in the proximal segment of the left renal vein (17.5 cm/s) was found to be significantly lower than that in both the distal left renal vein (121 cm/s) and the right renal vein (37 cm/s). The flow velocity in the proximal left renal vein decreased with decrease in the aortomesenteric distance and angle. Testicular vein diameters greater than 3 mm were statistically associated with decreased superior mesenteric artery angle. A significant association also was found between the left testicular vein diameter (in Valsalva maneuver) and inversion of flow. The decrease in flow velocity in the left renal vein proximal to the bifurcation of the superior mesenteric artery from the aorta supports the "nutcracker" theory. An association was found between the decrease of superior mesenteric artery angle and the increase in testicular vein diameter. Another association exists between the presence of reflux during Valsalva maneuver and increased testicular vein diameter. These finding were significant only for testicular vein diameter values greater than 3 mm.