We present the case of a male patient, 37 years old, who for two weeks had complained of right stabbing thoracic pain, cough with sero-muccous expectoration, 38ºC body temperature and dyspnea at exercise. He had taken temperature-lowering drugs, but without effect. Seven years before, he had been diagnosed with bronchial asthma, for which he was treated with a combination of inhalation corticosteroids and long-term action bronchodilators for about 3 years, with good evolution. He discontinued chronic asthma therapy for 2 years, but he was recommended to take Ventolin whenever necessary; he was free of bronchial obstructive bouts for about 2 years. Chest auscultation evidenced basal crackles (rales), while chest X-ray revealed a tendency of right basal condensation at the level of the posterior segment. The diagnosis was right basal pneumonia and therapy included antibiotics, muccolithic agents, and antipyretics. Evolution was good during the treatment and for another 2 weeks, when suddenly his condition worsened and was readmitted to the hospital in a more severe state than the first time. Differential diagnosis included: pulmonary neoplasm, pulmonary tuberculosis, pulmonary abscess. Complex investigations eventually elucidated the diagnosis.