The incidence of posterior urethral valves is estimated to be from 3:1000 to 8:1000 and this is one of the most common causes of obstruction of urinary tract in boys. About 13-17% of children with posterior urethral valves develop end stage renal failure. We present a 6-month-old boy with late diagnosis of posterior urtehral valves. Antenatal ultrasound investigation of the urinary tract was normal. A small degree of oligohydramnios was found during delivery. At the age of six months the boy was admitted to hospital because of urinary tract infection, hypertension (130/90 mmHg) and acute kidney injury (urea - 46 mg/dL, creatinine - 1.1 mg/dL, GFR - 35.5 mL/min/1.73 m2 ). Bilateral hydronephrosis and megaureters, low-capacity bladder with hypertrophied wall were seen on ultrasound examination. Voiding cystourethrograhy revealed vesicoureteral refluxes (III/V), hypertrophy of the bladder wall with numerous diverticula and dilated posterior urethra. During urethroscopy urethral valves were resected. Increased intravesical pressure (leak point up to 305 cm H2 O) was found on urodynamic test. Renal scintigraphy (99mTc-EC) revealed decreased intake of isotope in the left kidney (5%), and the right kidney intake was 95% ERPF. The patient was qualified for left-sided nephrectomy, which was postponed because of high leak point and high risk of worsening of vesicoureteral reflux to right kidney after nephrectomy. Anticholinergic and α-blocker treatment was started. At the age of 11 months left-side nephrectomy was performed because of recurrent urinary tract infections. After 3.5-year follow-up blood pressure, physical development, kidney function tests, and urinalysis are normal. Additionally to this investigation the significance of early diagnosis including prenatal (PUV) for further development as well as further therapeutic procedure is discussed.