Clinical staging is the attempt to determine the pathologic extent of a cancer by clinical tests (Whitmore). Traditionally, staging of prostate cancer has relied on the digital rectal examination, but ultrasonography, which provides an unprecedented picture of the gland, has become a valuable adjunct. The overall sonographic pattern helps to classify a tumor as "localized" or "extensive." A more detailed analysis yields information about the volume and location of the primary tumor; the presence, location, and extent of extracapsular extension; and the presence of seminal vesicle invasion. Comparison of sonograms with corresponding sections of radical prostatectomy specimens demonstrates that ultrasound complements the digital examination in determining by clinical tests the pathologic extent of a cancer.