Plasmablastic lymphoma (PBL) is a distinctive B-cell neoplasm which shows diffuse proliferation of large neoplastic cells, most of which resemble B-immunoblasts and have immunophenotype of plasma cells. PBL was originally described as a rare variant of diffuse large B-cell lymphoma (DLBCL) involving the oral cavity and occurring in the clinical setting of HIV and latent Epstein-Barr virus (EBV) infection. We report a case of 49 year old HIV positive male with PBL involving the colon and rectum, who initially presented with constipation and rectal bleeding. A CT scan was performed which showed peri-colonic infiltration, rectal wall thickening and involvement of iliac, inguinal and mesenteric lymph nodes. A subsequent colonoscopy showed multiple lesions in the colon and rectum. Biopsy of these lesions showed monotonous proliferation of large lymphoid cells with immunoblastic features and immunohistolochemical report was consistent with the PBL.