Neurogenic diabetes insipidus (NDI) approximately affects one of 25 000 people. The idiopathic type represents about 30% of all NDI cases (one of 75 000).1 The coexistence of primary NDI and systemic lupus erythematosus (SLE) is an exceptional fact that has not been previously described. We report two cases belonging to a series of 350 SLE patients (ARA criteria,1988).2 ### CASE 1 A 48 year old woman who had suffered from pulmonary tuberculosis in 1976. Ten years later she was examined because of a suspected myopericarditis. She also had a photosensitive malar erythema, oral ulcers, Raynaud’s phenomenon, vasculitic lesions on fingertips, Sjogren’s syndrome, and polyarthritis during one year. Blood count, complement, protein electrophoresis, rheumatoid factor, syphilis serological test, and renal function were normal. Antinuclear antibodies (ANA) were positive (1/160). Anticardiolipin …