From the very early period of development for transrectal ultrasound (TRUS), it has been noticed that a black homogenous echo pattern was occasionally observed in front of the prostate, in many patients with prostatodynia. Peeling (1982) named this as a "Sonolucent zone". Color Doppler sonography showed later that the finding correlated to the dilated capsular veins of the prostate. Recently advanced technology of 3D-MRI venography elucidated that a remarkable venous congestion was found in these patients, not only on the prostatic capsule, but also in the overall pelvis. According to our survey, 82% of patients diagnosed routinely as prostatodynia belonged to this new clinical entity, which may be called as "Intrapelvic venous congestion syndrome". The etiology of the syndrome will be discussed from the viewpoints of comparative anatomy and venous circulation.