Embolization of the left internal spermatic vein using spring-coils was performed in 20 patients with varicocele following pressure measurement of the left renal vein and inferior vena cava. During the follow-up of 16-24 months, there was no recurrence in 16 patients with pressure difference less than 3 mmHg; however, there were two recurrences in 4 patients with pressure difference greater than 4 mmHg and opacified adrenal or ureteral veins on venography. We conclude that a significant pressure difference between left renal vein and inferior vena cava, and opacification of adrenal or ureteral veins on left renal venography may be poor prognostic signs of recurrence of varicocele following embolization.