Urinary tract infections (UTIs) are caused by bacteria—most often, Escherichia coli. However, certain viruses, fungi, and parasites can also lead to infection. The infection can affect the lower and upper urinary tract including the urethra, prostate (in males), bladder, ureter, and kidney. Due to the progression of the disease and human anatomy, symptoms present differently among the sexes, as well as among different age groups. It is important to understand how these factors and others impact the pathophysiology of UTIs. Advanced practice nurses must have this foundation in order to properly diagnose patients.