Adenoiditis, i.e. the inflammation of the lymphatic tissue at the nasopharynx (adenoid), is a very common disease in enfants and younger children. Nowadays, with the use of nasopharyngeal endoscopy, it is believed that adenoiditis is also seen commonly in older children and adults. Objectives: To describe clinical characteristics of adenoiditis in older children and adults. Participants: 323 children and adults diagnosed endoscopically as having adenoiditis at the Thai Nguyen Pharmaco-Medical College Hospital. Methods: Descriptive epidemiological and interventional study. Results and discussions: Adenoiditis in older children and adults presents with a variety of clinical characteristics, commonly resulting in ear complications (56,2 percent). On patients with adnoiditis, there were frequently sino-nasal diseases (58,8 percent) and throat problems (59,4 percent). Endoscopic adenoidectomy showed satisfactory preliminary outcome.