Bladder diverticulum, an outpouching of the mucosa through the muscular wall of the bladder, is a multifactorial disease process that can be either acquired or congenital. Although small diverticuli are usually asymptomatic, a large diverticulum may result in hematuria, urinary tract infection, acute abdomen due to its rupture, acute urinary retention, or neoplasm formation. We describe the case of an elderly gentleman who presented to the emergency department with abdominal pain and was ultimately diagnosed with bladder diverticulitis, a disease not previously described in the literature.