Pelvic lymphoceles, occurred in patients undergone radical retropubic prostatectomy, are believed to increase the risk of deep venous thrombosis and so thromboembolic complications. The authors' aim is to evaluate the usefulness of pelvic ultrasonography in the diagnosis and in the possible early treatment of pelvic lymphoceles. Fifty-eight patients undergone radical prostatectomy and pelvic lymphadenectomy, between January '98 and December '99, underwent a pelvic ultrasonography in VII post-operative day. When a symptomatic or large (over 5 cm) lymphocele was found, it was treated with ultrasound (US) guided drainage. In the study, the following parameters were considered: lymphocele occurrence, size, location and treatment and thromboembolic complication. Statistical analysis was carried out with Fisher's exact test. Pelvic US showed a lymphocele in 23 out of 58 (40%) patients. Mean size was 5 cm. Deep venous thrombosis occurred in 4 patients, all with pelvic lymphoceles. No thromboembolic complications were recorded. In our experience, pelvic ultrasound has shown to be an easy e reliable tool for diagnosis and percutaneous treatment of pelvic lymphoceles.