The diaphragm is an unusual localization for disseminated erythematous lupus and is generally not recognized. We present the case of a 34-year-old woman who developed bilateral pain in the base of the thorax 15 days before hospitalization without any bronchial signs and NYHA stage II dyspnea. The patient's general health status remained satisfactory and the physical examination was normal except for diffuse inflammatory joint pain and cutaneous photosensitivization. The chest x-ray disclosed ascension of both hemidiaphragms with retracted lungs associated with bilateral basal atalectasia. The diagnosis of lupus with diaphragmatic involvement was retained due to the clinical presentation with diffuse joint pain, photosensitization with facial erythema, pericardial effusion and elevated antinuclear antibody and lymphopenia (1 100/mm3). Lung function tests revealed a restrictive syndrome. Oral corticosteroids 1 mg/kg/d enabled clinical and functional improvement. In light of this observation we discuss the pathogenic mechanisms of this uncommon localization of lupus and the difficulty of establishing a sure diagnosis.