Abstract Four cases of acute arthritis developed after parathyroidectomy, and pseudogout was suspected in each patient. All patients demonstrated typical chondrocalcinosis in radiographs of knees and wrists, and acute polyarticular arthritis developed in these affected joints. Intracellular rhomboidal crystals with weakly positive birefringence were characteristic of fluid obtained from the affected joints in two patients. The episode of acute pseudogout in these four cases, three of whom had no previous history of symptomatic joint diseases, indicates a possible relation between the changes in calcium metabolism after parathyroidectomy and the development of acute pseudogout.