Rituximab is an emerging treatment for thyroid eye disease. Rituximab effectively depletes circulating CD20+ B-lymphocytes; however, its effect on target tissues has not been well-studied. Failures of rituximab have been infrequently reported. The authors describe a patient treated with rituximab for thyroid eye disease who failed to respond to treatment, and underwent orbital decompression. Orbital fat samples and peripheral blood samples were evaluated for the presence of CD20+ B-lymphocytes. Complete depletion of CD20+ B-lymphocytes was demonstrated in both the orbit and the blood. This case demonstrates that rituximab effectively depletes orbital CD20+ B-lymphocytes, and this depletion was maintained for 2 months despite a clinical deterioration.