Malignant non Hodgkin's lymphomas in patients with acquired immunodeficiency syndrome are usually of high grade and have a B-cell phenotype. We describe two cases of rare lymphomas during acquired immunodeficiency syndrome: one case of pleomorphic T cell lymphoma with medium and large cell predominance, of high grade of malignancy, according to the updated Kiel classification, involving mainly the bone-marrow, and one case of low grade monocytoid B-cell lymphoma with bone-marrow extension, which is a rare condition in this type of lymphoma. These lymphomas seem to be a casual event during acquired immunodeficiency syndrome, but the immunodeficiency can be responsible of a more aggressive behavior.