Background: Retained appendicolith following appendicectomy, and can cause recurrent abscess in the abdomen and retroperitoneum.Case Characteristics: 11-yr-old boy who presented with subpulmonic abscess and pneumonia following appendicectomy for perforated appendicitis.Observation: Thoracotomy revealed a thick walled subpulmonic abscess surrounding an appendicolith along with a rent in the posterolateral aspect of the diaphragm.