Introduction:
Unilateral renal agenesis can occur as an isolated abnormality or can coexist with other anomalies of the urinary tract. Vesicoureteral reflux and hydronephrosis are the most common pathologies of the urinary tract. The less common pathologies are: megaureter, double kidney, ureterocele, ectopic kidney and hypospadiasis.

Case report:
We report a boy with a complex abnormality of the urinary tract: left renal agenesis and right ectopic kidney with megaureter and hydronephrosis, diagnosed at the age of 2.5 years. A routine ultrasonography of the abdomen was done because of the abdominal pain. There were no clinical symptoms associated with the urinary tract before this diagnosis. Based on dynamic scyntigraphy, urography and voiding cystourethrography a ureterovesical junction obstruction was found. At the age of 3 years, the transplantation of the ureter modo Cohen was performed. Despite the operation, hydronephrosis still persisted and the cortex of kidney was continuously getting narrower. At the age of 11.5 years arterial hypertension was diagnosed. At the age of 14.5 years, slightly elevated creatinine and isosthenuria were observed. During those twelve years of follow-up, urinalysis and culture of urine were normal.

Conclusions:
A child with unilateral renal agenesis and obstructive uropathy in the second kidney requires regular follow up with control visits and appropriate tests in outpatient nephrology clinic. Blood pressure monitoring and assesment of kidney function should be monitored. Urinary tract abnormalities in solitary kidney can progress to chronic renal disease and end-stage renal disease.