Asian variant intravascular lymphoma (AIVL) is a rare type of intravascular lymphoma that occurs in Asian populations. Syndrome of inappropriate antidiuretic hormone selection (SIADH) frequently occurs in patients with AIVL. Because it remains difficult to diagnose and has a poor prognosis, markers for early diagnosis are required. Although lactase dehydrogenase (LD) and soluble interleukin-2 receptor (sIL-2R) are diagnostic candidates, these markers do not appear to have been used often in prior studies. We present the case of an 87-year-old Japanese man with AIVL complicated by unexplained SIADH with a complaint of anorexia. Computer tomography showed splenomegaly but no lymphadenopathy. Elevated LD and sIL-2R were detected in the blood. The patient was diagnosed with AIVL through a random skin biopsy and was successfully treated with chemotherapy. When a patient presents with SIADH, we should actively look at or measure blood LD and sIL-2R for early diagnosis of ALVL. Further cases are warranted to determine these observations.