Phlebography of the internal spermatic vein in male patients suffering from infertility is a diagnostic procedure of low risk. In 432 patients examined for this condition, varicoceles were found, 67.5% of which occurred on the left, 13.8% on the right side. This fairly high number of varicoceles on the right side was surprising. It may be due to the technique, which requires standardisation and an experienced examiner in order to achieve a high rate of success. The possibility of a connection between unsatisfactory examination technique and unsatisfactory therapeutic results is discussed.