The final sample comprised 436 eligible participants from 231 hospitals in 22 states. The number of torsion cases nationally, estimated using a weighted analysis of the data, was 2248 cases (95% confidence interval [CI], 1950-2547 cases). Using census results, we estimated the total male population aged 1 to 25 years in 1998 to be 50.25 million. Using these 2 results, the incidence of testicular torsion is 4.5 cases (95% CI, 3.9-5.1 cases) per 100 000 male subjects per year in the United States. Within the age range considered, testicular torsion is most common in males aged 10 to 19 years, with an incidence of 8.6 cases (95% CI, 7.1-10.1 cases) per 100 000 male subjects per year. For comparison, the database contained 120 patients with benign or malignant testicular tumors. Using a weighted analysis, the number of such cases nationally was estimated to be 621 cases (95% CI, 300-912 cases). Using the population estimate, the estimated incidence of benign and malignant testicular tumors is 1.2 cases (95% CI, 0.7-1.8 cases) per 100 000 male subjects per year, and the disorder is most common in males aged 16 to 24 years, with an incidence of 2.8 cases (95% CI, 1.4-4.2 cases) per 100 000 male subjects per year. Figure 1 shows that 86% of testicular torsion cases occur in males older than 10 years (median age, 15 years), while 82% of testicular cancer cases occur in males older than 15 years (median age, 20 years).