We herein report a case of an 18-year-old female with Kawasaki disease who presented to the emergency department with epigastric abdominal pain and was subsequently found to have free fluid present in her abdomen visualized on bedside Focused Assessment with Sonography for Trauma (FAST) exam. Kawasaki disease is an acute vasculitis syndrome that primarily affects children and can have serious complications such as coronary artery aneurysms. The use of ultrasound in emergency departments is rapidly increasing, with the FAST being one of the most commonly performed bedside ultrasound examinations. FAST exams are most commonly performed in trauma patients as well as being part of the Advanced Trauma Life Support (ATLS) protocol. However, this case demonstrated that the FAST exam can also have application in other clinical scenarios and patient presentations where there is clinical suspicion of free intra-abdominal fluid.