Ki-1 monoclonal antibody is a well known marker for Reed-Sternberg cells in Hodgkin's disease, but also occasionally reacts with activated lymphoid cells of either benign or malignant nature. Recently, Ki-1 antibody positive Non-Hodgkin's lymphoma, usually of large cell and/or polymorphous type, has been reported in the lymph nodes, skin, soft tissue, and stomach, but not in the bone. We report a case of multifocal primary bone lymphoma in a seven-year old body involving the left shoulder and right frontal bone, which proved to be a large cell, polymorphous lymphoma, helper T-cell type expressing Ki-1 antigen.