Identical (monozygotic) female twins both simultaneously developed acute sarcoidosis with unusual manifestations. Additional to pulmonary involvement they both also had hypercalcaemia with compensated renal failure. When seen at the age of 33 years, these findings were more marked in one of them (case 2) than in the other, and she also had granulomatous conjunctivitis, while in the other one (case 1) the dominant sign was widespread lymph node enlargement. Both were also found by magnetic resonance imaging to have multiple lesions in the white matter, interpreted as the morphological correlate of neurosarcoidosis. But they caused clinical symptoms (visual disorder, unsteady gait) in only one sister (case 1). Treatment with prednisolone largely normalized the lung functions in case 2, completely in case 1, and renal functions in both. But when the daily prednisolone dose was reduced to below 10 mg, the pulmonary symptoms recurred. These observations indicate that even in chronic sarcoidosis acute episodes may occur, with involvement of multiple organs and other rare complications. The manifestations of the underlying disease in identical twins and the similarities of its course in the two sisters underline the possible role of genetic factors in the pathogenesis of sarcoidosis.