The role of myeloperoxidase deficiency has not been elucidated.<h4>Case presentation</h4>We present a case of 48-year-old female patient with acute lymphoblastic leukemia, stem cell transplant candidate, who developed a fever with lymphadenopathy and lung nodules, consistent with paracoccidioidomycosis infection, in whom a myeloperoxidase deficiency was later discovered. The gene discussed is MPO; the disease is acute lymphoblastic leukemia.