Background: Surgical removal of the tonsils, with or without adenoidectomy (adeno-/tonsillectomy), is a common ENT operation but the indications for surgery are controversial. Objectives: To determine the effects of tonsillectomy, with and without adenoidectomy, in patients with chronic/recurrent acute tonsillitis. Search strategy: The Cochrane Ear, Nose and Throat Disorders Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2008, issue 2), MEDLINE (1966 to 2008), EMBASE (1974 to 2008), bibliographies, and additional sources were searched for published and unpublished trials. The date of the last search was 11 April 2008. Selection criteria: Randomised controlled trials comparing tonsillectomy, with or without adenoidectomy, with non-surgical treatment in adults and children with chronic/recurrent acute tonsillitis. We included trials which used reduction in the number and severity of tonsillitis and sore throat as main outcome measures. Data collection and analysis: Two authors applied the inclusion/exclusion criteria independently. Main results: This review includes five studies: four undertaken in children (719 participants) and one in adults (70 participants). Good information about the effects of tonsillectomy is only available for children and for effects in the first year following surgery. Children were divided into two subgroups: those who are severely affected (based on specific criteria which are often referred to as the 'Paradise criteria') and those less severely affected. For more severely affected children adeno-/tonsillectomy will avoid three unpredictable episodes of any type of sore throat, including one episode of moderate or severe sore throat in the next year. The cost of this is a predictable episode of pain in the immediate postoperative period. Less severely affected children may never have had another severe sore throat anyway and the chance of them so doing is modestly reduced by adeno-/tonsillectomy. For them, surgery will mean having an average of two rather than three unpredictable episodes of any type of sore throat. The cost of this reduction is one inevitable and predictable episode of postoperative pain. The 'average' patient will have 17 rather than 22 sore throat days but some of these 17 days (between five and seven) will be in the immediate postoperative period. Whilst the concept of the 'average' patient is attractive, in practice, wide variability is likely. One reason why the impact of surgery is so modest, is that many untreated patients get better spontaneously. There is a trade-off for the physician and patient who must weigh up a number of different uncertainties: what proportion of my throat symptoms are attributable to my tonsils, and will I get better without any treatment? Similarly, the potential 'benefit' of surgery must be weighed against the risks of the procedure. Authors' conclusions: Adeno-/tonsillectomy is effective in reducing the number of episodes of sore throat and days with sore throats in children, the gain being more marked in those most severely affected. The size of the effect is modest, but there may be a benefit to knowing the precise timing of one episode of pain lasting several days - it occurs immediately after surgery as a direct consequence of it. It is clear that some children get better without any surgery, and that whilst removing the tonsils will always prevent 'tonsillitis', the impact of the procedure on 'sore throats' due to pharyngitis is much less predictable.