Background: The nutcracker syndrome represents a clinical condition caused by compression of the left renal vein (LRV) between the superior mesenteric artery (SMA) and the aorta. One of its manifestations is left-sided varicocele. The aim of this study is to determine the prevalence of nutcracker syndrome in patients with primary and recurrent high grade left-sided varicocele. Methods: Fifty patients with primary and recurrent high grade left-sided varicocele were enrolled in this study. Color Doppler ultra-sonography (US) of renal vessels was done and diameter of LRV and peak systolic velocity (PSV) were measured in renal hilum and in site of compression of LRV between SMA and the aorta and then magnetic resonance angiography (MRA) of renal vessels was done. Results: Thirty six patients (72%) had primary high grade varicocele and 14 patients (28%) had recurrent high grade varicocele. Twelve patients (33%) with primary high grade varicocele and seven patients (50%) with recurrent varicocele had evidences of NCS in color Doppler US and MRA. The differences of LRV diameter in NCS group and in patients without NCS were statistically significant (P<0.001).The differences of PSV in the LRV at the hilar portion in the NCS group and in the patients without NCS were not statistically significant.The differences of PSV in the LRV at the aortomesenteric portion in the NCS group and in the patients without NCS were statistically significant (P< 0.001).In all patients with NCS, MRA showed dilatation and compression of LRV at site of passage between aorta and SMA. Conclusion: NCS should be suspected in patients with high grade primary and recurrent varicocele.