It is reported that a clinical left varicocele is associated with loss of ipsilateral testicular volume. We have examined the loss of left testicular volume in infertile men with clinical left varicocele using ultrasound-derived measurements of testicular volume. We have reviewed the testicular volumes, maximum internal spermatic vein diameters, and the clinical reports of 404 men presenting for infertility evaluation at our institution between 1992 and 1996. Men with bilateral or subclinical varicoceles were excluded from the study. Subclinical varicoceles were diagnosed by the ultrasonographic demonstration of one or more veins having a maximal diameter of more than 3 mm. In men with clinical left varicocele, mean left testicular volume was less than right testicular volume (12.7 vs. 13.8 mL, P < .001). This finding was not observed in men without varicocele (12.3 vs. 12.6 mL, P > .05). In men with left varicocele, the difference between right and left testicular volume (right minus left) increased with increasing varicocele grade. Our data demonstrate that a left varicocele is associated with loss of left testicular volume. The results also show that the degree of left testicular hypotrophy is proportional to the clinical grade of the varicocele.