Open and arthroscopic synovectomies of the knee in patients with classic hemophilia were evaluated with regard to effectiveness in reducing bleeding episodes, the effect on range of motion (ROM), and roentgenographic progression of hemophilic arthropathy. Eleven patients underwent 13 synovectomies (eight open, five arthroscopic). The average follow-up periods were 7.9 years and 2.2 years for the open and arthroscopic groups, respectively. Both procedures significantly reduced recurrent hemarthroses. Knee ROM in the open synovectomy group was decreased or unchanged in 75% and minimally increased in 25%, whereas there was an increased in 80% and a decrease in 20% of the knees in the arthroscopic group. Furthermore, 62.5% of the knees required manipulation to improve ROM in the open synovectomy group, versus 0% in the arthroscopic group. Hemophilic arthropathy progressed in most knees in both groups. The arthroscopic group had a longer operative procedure (122 versus 59 minutes), but required less hospitalization (9.4 versus 23.1 days) and 25.6% less Factor VIII replacement. Both techniques reduce hemarthroses. There is usually a net loss of ROM with the open versus a net gain with the arthroscopic procedure, and roentgenographic progression hemophilic arthropathy is slowed but not halted after synovectomy.