We report a case of calcium pyrophosphate dihydrate crystal deposition disease (CPDD) presenting as an acute polyarthritis. A 66-yr-old woman was admitted with a 5-day history of fever and multiple joint pain including wrists, elbows, shoul-ders, knees, and ankles developed 5 days before admission. Her plain radiographs of wrists, elbows, shoulders, knees, and ankles showed chondrocalcinosis. The pubic symphysis, lumbar intervertebral discs, and both hip joints, which were asymptomatic, also had calcium deposits. The compensated polarized microscopic examination of the joint fluid, aspirated from the right knee revealed intracellular and extracellular weakly positive birefringent crystals, confirming the CPDD. This case showed that CPDD may manifest as an acute polyarthritis mimicking acute onset rheumatoid arthritis.