Periodic fever, aphthous stomatitis, pharyngitis, and cervical adenitis (PFAPA) syndrome is the most common recurrent fever syndrome in children. Children with PFAPA have fevers that last 3-7 days and recur every 3-6 weeks, in the presence of the symptoms listed in the disease name. Although many different therapies are used to treat PFAPA, it is difficult to compare them because there are no reliable tests to measure disease activity. A disease activity index is a scoring system that accounts for different signs and symptoms of a disease to determine disease severity. The goal of this study is to validate the already established Auto-Inflammatory Diseases Activity Index (AIDAI) as an activity measure for PFAPA. This would be helpful to conduct further studies to compare treatments for PFAPA with the goal of treating children on a more individual level.