Reports of neoplasia in reptiles are becoming more common in the literature, and tumors of all major body systems have been documented. This report describes a case of disseminated lymphosarcoma in a 5-yr-old male Asian water dragon. The dragon was presented for a 5-wk history of decreased appetite, lethargy, watery eyes and diarrhea. According to the owner, it also had mouth rot on and off for 3 yr. The dragon was emaciated and almost comatose on admission. It was euthanatized shortly afterwards and sent for post mortem examination. Neoplastic lymphocytes were found in the liver, kidneys, testes, tongue and medullary canals of the mandible and maxilla. The tumor was further characterized as a T-cell lymphosarcoma by immunohistochemical staining of spleen and kidney with antibodies directed against CD3, a T-lymphocyte specific antigen. To our knowledge, determination of the origin of a reptilian lymphoid tumor has never before been documented.