To study the effectiveness of adenoidectomy and of the placement of tympanostomy tubes in the treatment of chronic otitis media with effusion, we randomly assigned 578 children, aged four through eight years, to receive bilateral myringotomy and no additional treatment (Group 1), placement of tympanostomy tubes (Group 2), adenoidectomy (Group 3), or adenoidectomy and placement of tympanostomy tubes (Group 4). The 491 children who underwent one of these treatments were examined at six-week intervals for up to two years. The mean time spent with effusion of any type in either ear over the two-year follow-up in the four groups was 51, 36, 31, and 27 weeks, respectively (P less than 0.0001), comparing Group 1 with each of the other groups. Hearing was equivalent in Groups 2, 3, and 4, and was significantly better than in Group 1. The most frequent sequela, purulent otorrhea, occurred one or more times in 22, 29, 11, and 24 percent of the subjects in Groups 1, 2, 3, and 4, respectively (P less than 0.001). Adenoidectomy plus bilateral myringotomy lowered the overall post-treatment morbidity (as measured by hearing acuity in the most severely affected ear [P = 0.0174] and the number of surgical retreatments required [P = 0.009]) more than did tympanostomy tubes alone and to the same degree as did adenoidectomy and tympanostomy tubes. We conclude that adenoidectomy should be considered when surgical therapy is indicated in children four to eight years old who are severely affected by chronic otitis media with effusion.