Adenoids (nasopharyngeal tonsil) are a mass of lymphoid tissue situated posterior to the nasal cavity, in the roof of the nasopharynx, where the nose blends into the throat. In the back of the nose there is a small pad of tissue, whose job is to keep out infection. When this tissue deals with repeated infections, it can become chronically enlarged causing a condition called adenoids. They seldom occur after puberty.