X-linked agammaglobulinemia (XLA) is a primary immune deficiency characterized by recurrent bacterial infections and profoundly depressed serum immunoglobulin levels and circulating mature B cells. We describe a 12-year-old boy with XLA and enthesitis-related arthritis (ERA). To date, there has been a paucity of reports of noninfectious inflammatory arthritis in children with XLA. This case illustrates that functional B cells and/or immunoglobulin are not required for ERA pathogenesis. In addition, this case suggests a possible link between immune deficiency, immune dysregulation, and rheumatic illness.