Hypercalcemia due to malignant tumors including malignant lymphomas is relatively common. Among cancer patients with hypercalcemia, humoral hypercalcemia of malignancy is the most common and accounts for about 80% of all cases with hypercalcemia. 1,25-dihydroxyvitamin D
3
(1,25(OH)
2
D
3
)-mediated hypercalcemia is relatively rare. Although malignant lymphoma has been also reported to cause 1,25(OH)
2
D
3
-mediated hypercalcemia, it is not known whether there is any association between 1,25(OH)
2
D
3
-mediated hypercalcemia and any specific histological type of malignant lymphoma. We herein report a case of an anaplastic large cell lymphoma (ALCL), anaplastic lymphoma kinase (ALK) -negative with 1,25(OH)
2
D
3
-mediated hypercalcemia, which has never been previously reported. An 80-year-old Japanese man was admitted to our department due to acute exacerbation of hypercalcemia. He was diagnosed with ALCL, ALK-negative. Serum 1,25(OH)
2
D
3
level was high and seemed to be associated with the lymphoma because the serum calcium and 1,25(OH)
2
D
3
levels improved in response to chemotherapy. Histological findings showed that many CD68 positive macrophages were observed in the microenvironment of tumor cells. Lymphoma cells or tumor microenvironmental cells may produce 1,25(OH)
2
D
3
because several previous reports showed the source of 1,25(OH)
2
D
3
can be either lymphoma or tumor microenvironmental cells. Moreover, because 1,25(OH)
2
D
3
-mediated hypercalcemia has been reported regardless of the specific histological type of lymphoma, tumor microenvironmental cells may be involved in this condition. However, we could not identify the source of 1,25(OH)
2
D
3
in this case. The association between 1,25(OH)
2
D
3
production and prognosis in malignant lymphomas is yet unknown; further studies are needed to elucidate the clinical characteristics of malignant lymphoma with 1,25(OH)
2
D
3
-mediated hypercalcemia.