We assessed the value of ultra sonography in diagnosis and grading the alterations in canalization of seminal pathways. After clinical examination and semen analysis, we studied 4100 patients by scrotal US with sector mechanical (7.5 MHz) probe with water bag and by transrectal US for prostatic vesicular region evaluation with 5-6.5 MHz linear probe (lately we used biplanar probe). In three cases, we performed us guided aspiration and contrast media injection of prostatic cavity. In 63 cases (1.53%) we found developmental malformations of seminal vesicles. The abnormality was bilaterally in 33% and it was associated with malformations of urinary tract in 17.46%. Other malformations were found in 0.12% cases. Ultrasonography was always able to establish obstruction level and type, and the possible associated abnormalities. US permitted to avoid or to restrict testis biopsy or vasoseminal vesiculogram. Ultrasonography is eventually able to guide second level diagnostic examination (aspiration biopsy and contrast media injection of prostatic cysts) and endourethral approach to drainage.