Primary hyperparathyroidism is a disease with increased cell proliferation and enhanced PTH secretion due to the escape from negative feedback by calcium ion in parathyroid cells for their tumorization. Involvements of several gene abnormalities have been demonstrated in the pathogenesis of parathyroid tumor. First, an activation of cyclin D1 gene by the translocation of 11 chromosome was found as one of the cause of parathyroid tumorigenesis. Moreover, mutation of multiple endocrine type 1 gene is the most frequent as a genetic cause of sporadic parathyroid tumor. Its related tumor is developed by an inactivation mutation of tumor suppressor gene. Parafibromin, calcium-sensing receptor, vitamin D receptor, Klotho and RET might be related to the tumorigeneis of parathyroid tumor.