PURPOSE: To report a case of chronic, progressive unilateral blepharoptosis in a 73-year-old woman with Waldenstrom's macroglobulinemia. METHOD: Case report. A biopsy was performed on a thickened and indurated tarsal plate that we believed had resulted in mechanical blepharoptosis. RESULTS: Histologic and immunohistochemistry studies of the biopsy specimen demonstrated a lymphoplasmacytoid cell infiltrate with monoclonal antibodies consistent with Waldenstrom's macroglobulinemia. CONCLUSION: Involvement of the tarsal conjunctiva and tarsus in Waldenstrom's macroglobulinemia is a newly recognized cause of eyelid thickening and ptosis, (Am J Ophthalmol 1998;126: 315-317, (C) 1998 by Elsevier Science Inc. All rights reserved.).