Study Objective: To determine the value of clinical history and preoperative coagulation tests.Design: Prospective, multicenter clinical investigation.Setting: Twenty-four centers over a one-year period.Patients: 1,706 children scheduled for tonsillectomy. In 1,479 out of 1,706 children, studied age was ranged from 9 months to 15 years. Indications for surgery were tonsillar infection 54%, sleep apnea 33%, or both 13%. Surgical dissection was performed in 1,284 cases (88%) and sluder technique in 172 cases (12%).Measurements and Main Results: Clinical history of bleeding, preoperative coagulation tests, and perioperative bleeding were recorded. Clinical history of bleeding was positive in 13 patients; clinical history cannot predict abnormal coagulation tests. Coagulation tests were abnormal in 57 children (4%). Only 8 patients had disease-induced bleeding; five children had a preoperative correction of the deficiency in factor of coagulation or received desmopressin acetate prior to surgery in the case of von Willebrand's disease. Bleeding that occurred during the intraoperative period was assessed as abnormal by the surgeon in 101 children (7%) and during the postoperative period in 50 children (3%). Univariate analysis showed a relationship between intraoperative bleeding and age (p < 0.001), sluder technique (p < 0.001), and abnormal preoperative coagulation tests (p < 0.05). Multivariate analysis showed the probability that bleeding was linked to the center where the surgery took place, the technique used, i.e., sluder technique, and the child's age, i.e., the older children.Conclusions: Preoperative assessment based on the history of bleeding cannot predict abnormal laboratory tests. Neither the history of bleeding or laboratory tests can predict postoperative bleeding.