Objective To present cases with complicated urinary tract infections and the most frequent causes of infection.

Methods Included in the study are cases with urinary tract anomalies and uroinfections. The diagnosis has been estabilished by clinical examination, microbiologic examination of urine, ultrasound examination of the urinary tract, excretory urography and voidin cisturethrography.

Results We have analysed 130 children with urinaty tract anomalies. We performed a microbiologic examination of urine and identified the cause. The results of the study show that examined samples in 13.8% of the cases were sterile and in 86.2% of cases were positive. From the isolated organisms E. coli was the most frequent cause of infection (53.8%), followed by the infections caused by Klebsiella (19.2%), Proteus (13.0%), Citrobacter (1.54%) and Pseudomonas (0.77%).

Regarding the type of the anomalies of the urinary tract the results of the microbiologic examination shows that at obstruction of the ureteropelvic junction E. coli is the most commonly isolated (65.1%). Obstructive uropathy associated with calculi in 45% of the cases were sterile, in 40% of the cases E. coli was isolated, than Proteus (15%) and Klebsiella (5%). At vesicoureteral reflux E. coli was isolated (61.8%), followed by Klebsiella (17.6%).

From 16 patients with megaureter, in 50% of the cases Klebsiella was isolated and in 37.8% E. coli.

Conclusion The study has shown that the most frequent cause of complicated urinary tract infections is E. coli, followed by Klebsiella while the other causes are present only in small percentages.