The aim of the study was to analyze the gene expression of JUN and CCND1 in a group of parathyroid tissues obtained from patients with primary hyperparathyroidism in comparison to hyperplastic parathyroid and normal/atrophic parathyroid tissues by real-time quantitative PCR. Our goal was to validate the conclusion of Forsberg et al (2005) who reported overexpression of JUN in parathyroid adenomas by a joint microarray and QPCR study.Material and methods. The analysis of JUN, CCND1 was carried out by QPCR in 14 parathyroid adenomas, 8 hyperplasia cases and 50 normal/atrophic parathyroid samples taken intraoperatively. Expression of the examined genes was normalized to the reference index (geometric mean of reference genes expression: EIF3S10, UBE2D2, ATP6V1E).Results. We observed a decrease of JUN expression in parathyroid adenomas in comparison to both normal/atrophic and hyperplastic parathyroids. The fold change value was 0.71 in comparison of adenomas to normal/atrophic samples (p = 0.044) and 0.75 to hyperplastic glands (p = 0.003). For CCND1 we observed one case of parathyroid adenoma with a very clearly increased expression, while 3 adenomas (21.4% of all adenomas) exhibited the increase over the highest value seen in normal parathyroids (fold change = 3.52).Conclusions. In parathyroid adenomas we were not able to confirm any overexpression of JUN gene, as suggested by the previous study. On the contrary, we observed a distinct inhibition of JUN RNA expression in comparison to non-neoplastic parathyroids. For CCND1 gene overexpression in parathyroid adenomas, we report the frequency of 21.4%.