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Background: Spontaneous rupture of tendon is a rare disease that often occurs following an underlying disease or drug usage. However, the association of this condition with primary hyperparathyroidism has rarely been reported. Case: In a case-study, two cases of spontaneous tendon rupture associated with primary hyperparathyroidism are reviewed. The first one is a middle-aged woman that due to bilateral patellar tendon rupture is operated for secondary repair and augmentation of tendons. The second one is a middle-aged man with unilateral triceps brachii tendon rupture who has been operated for primary tendon repair. Conclusion: Since paramount force is needed for tendon rupture, in spontaneous tendon rupture cases, patient evaluation for detecting underlying diseases and drug usage is necessary. In cases that the history of an underlying disease is not indicated, evaluation of serum level concentrations of Ca, P, ALP, and PTH is recommended for contraindication of primary hyperparathyroidism.