Urinary tract infection (UTI) in infants and babies is still a challenging problem. The aim of the study was the clinical analysis of children under three years of age with UTI, hospitalised in The Department of Paediatrics, Medical University of Lodz in 2000-2001. The study included 91 children (45 girls and 46 boys), aged 1-36 months; 10 months on the average. Acute UTI was observed in 29% of children, recurrent UTI was diagnosed in 71% of patients. Voiding cystography was performed in 82% of children. Among 28/91 cases of vesicoureteral reflux, 36% were unilateral and 64% were bilateral. Vesicoureteral reflux grade 2 was most frequent (64%) in patients with UTI. The most common pathogen was Escherichia coli. The obtained results demonstrate the necessity of early imaging diagnosis of the urinary system in infants and babies with UTI. Patients under three years of age with UTI require hospitalisation and performance of early diagnostic examinations of the urinary tract.