We have studied the knees of 50 patients with hemophilia A, using ultrasound (US) when conventional radiology did not detect any secondary osseous changes. The sonographic images were compared with those obtained from 50 healthy controls. The mean age of this series was 14.6 years. Our results suggest that sonography as a diagnostic technique in the initial stages of hemophilia permits differentiation between suprapatellar effusion and synovial thickening. It also reveals early cartilaginous involvement.