Modern diagnostics of kidneys and urinary tract defects in children covers a wide range of examination, first of all of diagnostic imaging. They are designed mainly to detect specific diseases but they are also useful in monitoring treatment, predicting the risk of developing chronic kidney disease and its multiorgan long-term effects. The correct interpretation of images of the urinary system requires the knowledge of kidneys, ureters, bladder and urethra, anatomy with all kinds of the most common varieties of their construction. Malformations of the urinary tract are the most common congenital anomalies. Most of them are asymptomatic, which may hinder the identification and implementation of appropriate procedure. Early diagnosis and appropriate treatment of urinary tract defects is essential in prognosis, gives a chance to maintain renal function, and thus to normal development of the child. The article describes the cases of clinical diagnostic steps successively achieved in particular health problem, in which the key element proved to be computed tomography (TK). TK allows a good assessment of the anatomy of the kidney and urinary tract. Progress in the field of diagnostic imaging and the prospect of new technical possibilities of tests gives clinicians many diagnostic and therapeutic opportunities and helps to improve the standard of care in children with nephrological problems.