Purpose: Primary hyperparathyroidism (PHPT) is caused by typical adenoma (TA), multiglandular disease (MD), or parathyroid carcinoma (PC), and in a smaller percentage of cases by atypical parathyroid tumor (APT). The objective of this study is the retrospective analysis of clinical features and parathyroid hormone (PTH)/calcium response to surgery in patients who underwent parathyroidectomy for symptomatic PHPT with histological evidence of APT. Methods: We retrospectively reviewed our institutional experience in the management of PHPT from January 2016 to December 2021 focusing on those patients presenting APTs. We analyzed the clinical features of this disease and PTH/ calcium response to surgical treatment in APTs compared to the other pathological conditions causing PHPT. Results: In a cohort of 125 patients with PHPT we found 112 TAs (89.6%), 6 APTs (4.8%), 6 PCs (4.8%), and only 1 MD (0.8%). APTs in comparison to other parathyroid diseases showed peculiar features such as adhesion to the surrounding structures and a frequent intrathyroidal location, which may justify thyroid loboistmectomy adopted in most of the observed cases. APTs showed significantly higher preoperative PTH values compared to TA + MD and were relevant to PC. Conclusion Due to its rarity, there is a lack of specific indications in the management of APTs. Biochemical features observed in APT and PC can be related to similar biological behavior. However, some specific features observed preoperatively in some cases of PHPT might suggest presence of an APT, which could be helpful mostly in surgical and postoperative management. Further studies are required to confirm the results of the present preliminary report.