This paper explores outcomes associated with the tonsillectomy operation using multiple control groups and a large claims-based data bank from the Canadian province of Manitoba. Given the difficulty of conducting large-scale clinical trials of common surgical procedures, the use of multiple methods for evaluating such interventions is both advocated and implemented in this study. When the data are restricted to respiratory diagnoses, the findings suggest that, on the average, tonsil surgery saves between one half and one and a half episodes of illness per patient over the two years after surgery. Such savings are much more pronounced among individuals having several tonsillitis episodes in the preoperative year. However, when all medical claims are considered, the estimated savings from the tonsillectomy operation are somewhat reduced. Individual variation in predisposition to "see the doctor" appears to account for such results; visits about conditions other than respiratory take up much of the "savings" produced by tonsil surgery. The findings are discussed in terms of the costs and benefits of the tonsillectomy operation, and future research needs are outlined.