The obstruction caused by posterior urethral valves may be responsible for profound dysfunction of the entire proximal urinary tract. The pathophysiologic relations between the valves and function of the ureterovesical junction and upper urinary tract are key in determining the need for upper tract surgery. In most cases, function of the ureters and ureterovesical junction is directly related to high intravesical pressure and will normalize when pressures drop after valve destruction. However, upper tract function remains abnormal in some cases and leads to complications that necessitate early ureteral and upper tract surgical intervention. The second crucial relation in the management of patients with posterior urethral valves is that between renal dysfunction and urinary tract obstruction. The surgeon is compelled to maximize the potential for renal function. The relation between renal dysplasia, obstructive uropathy, and urinary tract obstruction complicates the management of patients with posterior urethral valves and challenges us to develop new methods to measure potential renal function. Patients born with posterior urethral valves are treated initially with bladder drainage, which is undertaken by placement of a urethral catheter at the time diagnosis is made with the voiding cystogram. During this initial period of evaluation and stabilization, the patient's medical status is optimized, giving the surgeon information concerning renal function and prognosis to allow the most efficient surgical management. In almost all cases, posterior urethral valves are destroyed primarily, most often by transurethral fulguration. This usually leads to rapid improvement of bladder, upper tract, and renal function. When primary fulguration is not advisable, drainage through a vesicostomy is a useful alternative. Utilizing either method, low-pressure bladder drainage is a primary goal in the initial management of patients in most centers. As with many problems in surgery, our ability to accurately identify patients who would benefit from surgery is more limited than our surgical effectiveness. Voiding cystograms allow us to diagnose reflux and to follow bladder emptying and function. Serial ultrasound scans, nuclear medicine scans, and pressure-perfusion studies give us insight into upper urinary tract function. Too often, however, limitations of the patient's condition and size and the severe degree of urinary tract abnormalities make the results difficult to interpret. Although diagnostic tests are invaluable in making decisions about upper tract surgery in patients with posterior urethral valves, these decisions are most often based on the classic clinical urologic problems of urinary extravasation, obstruction, infection, reflux, and azotemia.(ABSTRACT TRUNCATED AT 400 WORDS)