Patients with AIDS have become more and more prevalent. Therefore, the onset of diseases that coexist with this condition must be studied in order to establish proper diagnosis and treatment. We report a case of a patient who reported with loss of strength in the lower limbs and a progressive worsening in his clinical picture. He was diagnosed with acute lymphocytic leukaemia, an unusual form of association with the AIDS condition. Despite the diagnosis, he evolved into pulmonary sepsis and so staging and chemotherapy treatment could not be performed.