The case of a 20 years old male who was admitted to our hospital for lasting fever and pain in the right shoulder is reported. During his hospitalization the patient developed acute respiratory failure with patchy infiltrates of the lower lobes in chest radiograph. The patient was mechanically ventilated. The laboratory tests, which followed, helped us to establish the diagnosis of acute lupus pneumonitis and to administer the appropriate treatment. The patient was successfully discharged from the hospital. Acute lupus pneumonitis is a rare manifestation of Systemic Lupus Erythematosus, requires aggressive diagnostic approach and has generally high mortality rate. Pneumon 2000, 13 (3): 236-240