Objective: To examine at the population level which children were operated on for recurrent acute otitis media episodes, how ill they were, and what factors affected the operation rate. Design: A retrospective birth cohort with an approximate 2-year follow-up. Infection data were gathered from medical records, and background information was gathered from questionnaires. Setting: Primary health care centers, hospitals, and private practices in 10 randomly selected local government districts in the two northernmost provinces of Finland. Subjects: A random sample of 2512 children from the cohort. Outcome Measures: Adenoidectomy and/or tympanostomy tube insertion. Results: Only one of 10 of those with actual recurrent disease (greater than or equal to 4 episodes) had been operated on, and three of every five children operated on, in fact, had rather few episodes. The operation rate among those children with only a few episodes was increased by factors such as consulting an ear, nose, and throat specialist (risk ratio [RR], 13.0; 95% confidence interval [CI], 7.6 to 22.2); parental exaggeration of the episodes (RR, 6.7; 95% CI, 3.8 to 11.9), having the first episode under 6 months of age (RR, 4.5; 95% CI, 2.5 to 7.9); recurrent respiratory tract infections (RR, 3.3; 95% CI, 1.9 to 5.7); male sex (RR, 2.6; 95% CI, 1.4 to 4.6); urban domicile (RR, 2.4; 95% CI, 1.1 to 4.9); and day care (RR, 2.1; 95% CI, 1.1 to 3.8). The decision to operate was more or less a random phenomenon among those children with numerous episodes. Conclusions: Physicians at the primary care level should be familiar with these pitfalls concerning patient selection so that the operations are targeted at those children who are most seriously ill.