Urinary tract infections or UTIs are the generic name given to any infection involving the urinary tract. Most commonly these infections are caused by bacteria, but in more unusual circumstances may be caused by yeast or viruses. Urinary tract infections are separated into those infections limited to the bladder (cystitis) and those that involve the kidneys (pyelonephritis). When discussing infections of the urinary tract in pediatric patients, it is important to note whether the infections are associated with a fever. It is those infections associated with fevers that are most concerning, as these may be associated with anatomic abnormalities placing patients at an increased risk of kidney infections.