During the past 4 years the author experienced 2 crises of parathyroid adenoma which were diagnosed by the histopathological examination of the tumor mass removed by the surgical operation. The first case was a 22 year old male. The adenoma was located at the right lower portion of the thyroid area, and weighed 5.2 grams. The second case was a 39 year old female, and the tumor was also located at the right lower portion of the thyroid area, and weighed 2.0 grams. Microscopically, the first cases showed predominantly chief cells, mixed with small number of transtional and oxyphilic cells. The second case showed mainly chief cells, but some number of water clear cells transitional cells and oxyphilic cells were also found. A brief review of the literature and a discussion on the clinicopathological correlations were made.