We report three lymphoma patients in whom the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) was observed during the course of lymphoma-associated hemophagocytic syndrome (LAHS). The clinical course was devoid of any known mechanism for SIADH which could be attributable to lymphoma or antineoplastic treatment. Alternatively, high serum levels of interleukin-1 beta and tumor necrosis factor-alpha, which stimulate the secretion of antidiuretic hormone, may have contributed to the development of SIADH in our patients, who were receiving glucocorticoids. In conclusion, LAHS patients should be considered to be at high risk for SIADH.