Bacillus Calmette-Guerin (BCG) has been studied in various cancers for its immune modulation. Although the mechanism is yet to be completely understood, we do have positive experiences in many oncological cases. Hereby, we present a case of an 82-year-old male with acute myeloid leukemia (AML) post allogeneic Stem Cell Transplants (AlloSCT) as a salvage therapy, now in remission, who presented with hematuria. Workup confirmed non-muscle invasive Bladder Cancer (NMIBC), for which he was treated with nine sessions of intravesical BCG therapy. During BCG treatment, the patient developed gradually increasing lymphocyte counts. Flowcytometry of a peripheral blood sample showed polyclonal cell lymphocytosis with CD8+ T-cell expansion. Although further work up his lymphocytosis to be polyclonal, it has persisted at follow-up for the last 4 years. Also, we did not find any evidence of leukemia recurrence at follow-up prompting us to associate the BCG use for this patient and it is role as immunomodulation to keep AML disease in remission.