The most common cause of enlarged tonsils in adults is recurrent inflammation of the tonsils, or chronic inflammation that causes the tonsillar glands to become enlarged and swollen. In addition, tonsillar lymphoid hyperplasia, tonsillar cysts, tonsillar papillomas and tonsillar tumours can also cause swollen tonsils, and histopathological examination is often required to identify these causes. It is advisable to seek prompt medical attention.