In previous clinical trials involving children severely affected with recurrent throat infection (7 or more well-documented, clinically important, adequately treated episodes of throat infection in the preceding year, or 5 or more such episodes in each of the 2 preceding years, or 3 or more such episodes in each of the 3 preceding years), we found tonsillectomy efficacious in reducing the number and severity of subsequent episodes of throat infection for at least 2 years. The results seemed to warrant the election of tonsillectomy in children meeting the trials' stringent eligibility criteria but also provided support for nonsurgical management. We undertook the present trials to determine 1) whether tonsillectomy would afford equivalent benefit in children who were less severely affected than those in our earlier trials but who nonetheless had indications for tonsillectomy comparable to those in general use, and 2) whether, in such children, the addition of adenoidectomy would confer additional benefit. We conducted 2 parallel randomized, controlled trials in the Ambulatory Care Center of Children's Hospital of Pittsburgh. To be eligible, children were required to have had a history of recurrent episodes of throat infection that met standards slightly less stringent than the standards used in our earlier trials regarding either the frequency of previous episodes or their clinical features or their degree of documentation, but not regarding >1 of those parameters. These reduced standards were nonetheless more stringent than those in current official guidelines, which list "3 or more infections of tonsils and/or adenoids per year despite adequate medical therapy" as an indication for tonsillectomy or adenotonsillectomy. Of 2174 children referred by physicians or parents, 373 met the current trials' eligibility criteria and 328 were enrolled. Of these, 177 children without obstructing adenoids or recurrent or persistent otitis media were randomized to either a tonsillectomy group, an adenotonsillectomy group, or a control group (the 3-way trial), and 151 children who had 1 or more such conditions were randomized to either an adenotonsillectomy group or a control group (the 2-way trial). Outcome measures were the occurrence of episodes of throat infection during the 3 years of follow-up; other, indirect measures of morbidity; and complications of surgery. By various measures, the incidence of throat infection was significantly lower in surgical groups than in corresponding control groups during each of the 3 follow-up years. However, even among control children, mean rates of moderate or severe episodes were low, ranging from 0.16 to 0.43 per year. Adenotonsillectomy was no more efficacious than tonsillectomy alone. Of 203 children treated with surgery, 16 (7.9%) had surgery-related complications of varying types and severity. The modest benefit conferred by tonsillectomy or adenotonsillectomy in children moderately affected with recurrent throat infection seems not to justify the inherent risks, morbidity, and cost of the operations. We conclude that, under ordinary circumstances, neither eligibility criteria such as those used for the present trials nor the criterion for surgery in current official guidelines are sufficiently stringent for use in clinical practice.