Purpose: To review the natural history of mild hemophilia (factor VIII or IX level >5% and <50%), including presentation and diagnosis, characteristics of bleeding episodes, and therapy, at two hemophilia treatment centers.Methods: Inpatient and outpatient records of 55 patients <17 years old with factor VIII or IX levels of 5 to 50% were reviewed and bleeding episodes for which medical attention was sought were analyzed.Results: Five of the 55 patients were girls. Girls and patients with no family history of hemophilia were diagnosed at 5.5 and 5.3 years of age, respectively, compared to 2.8 years overall. Thirty-five patients were diagnosed because of a positive family history. No bleeding occurred in 18 patients; 190 bleeding episodes occurred in 37 patients. Most bleeding occurred in muscle/soft tissue (101 episodes) or joints (57 episodes) and were associated with trauma (174 episodes).Conclusions: Mild hemophilia may affect females more often than is appreciated. Delays in diagnosis and treatment may occur unless the variability in presentation is recognized.