This chapter focuses on urinary tract infections (UTIs) in adults and children. UTIs are more common in women than in men. One in three women will have a UTI before 24 years of age. Uncomplicated UTIs generally respond well to antimicrobial therapy, whereas complicated UTIs are often associated with multidrug resistance (MDR) pathogen in patients with other comorbidities. Urine culture is usually not needed for patients with an uncomplicated UTI because a treatment response to antimicrobial therapy will have occurred before the results become available. In infants, signs suggestive of a UTI are high temperature without another source for more than 24 hours in boys or more than 48 hours in girls. The diagnosis of a UTI can be suspected on the basis of changes in the urinalysis, but is verified by culture of a reliable urine sample. Management including voiding cystourethrogram (VCUG) indication and long-term chemoprophylaxis against UTI in patients who have vesicourethral reflux (VUR).