We describe a malignant lymphoma arising in the kidney that exhibited clinical and histologic features of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT). Clinically, the neoplasm involved the kidney and one perirenal lymph node (stage IIE) and did not recur or disseminate following nephrectomy, lymphadenectomy, and local radiation therapy. Histologically, the neoplasm recapitulated the features of low-grade B-cell lymphomas of MALT at other sites. The neoplastic cells resembled centrocyte-like cells, some of which formed lymphoepithelial lesions with renal tubules, and reactive lymphoid follicles were scattered within the neoplasm. The neoplastic cells expressed monotypic cytoplasmic Ig kappa. Low-grade B-cell MALT lymphomas arising in the kidney are rare. Their occurrence further demonstrates the diversity of anatomical sites that may be involved by MALT lymphomas. In addition, this neoplasm also had histologic and cytologic features resembling those of monocytoid B-cell lymphoma, supporting the hypothesis that low-grade B-cell lymphomas of MALT and monocytoid B-cell lymphomas are closely related and may be two morphological manifestations of the same neoplasm.