Whereas radiographic lesions of the sacroiliac joints are common in patients with calcium pyrophosphate deposition crystal disease, they are rarely accompanied with clinical symptoms. We report two cases of acute sacroiliitis probably due to calcium pyrophosphate dihydrate deposition disease. The patients were a 53-year-old man and an 82-year-old woman with chondrocalcinosis in other joints and presence on computed tomography studies of the sacroiliac joints of sclerosis and irregularities of the joint margins with a thin linear calcific deposit within the joint. Both patients recovered fully under therapy with colchicine, analgesics and rest. These two cases suggest that acute sacroiliitis can be caused by calcium pyrophosphate dihydrate crystal deposition disease.