In our study we presented patients that developed primary hyperparathyroidism, that could be caused by typical adenoma (PA), atypical adenoma (APA), hyperplasia and cancer (PC). According to our research, most cases suffered the symptoms of hypercalcemia due to hyperplasia and typical adenoma (PA) that are benign conditions. The therapeutic outcome for this patients’ group was very satisfactory with a very high rate of curability [1, 3, 28]. On the other hand, patients with atypical parathyroid adenomas (APA) are at higher risk of development of parathyroid carcinoma (PC), thus it is very important from a surgical point of view to resect all of the tumor to prevent development of malignancy [2, 7, 33]. Patients will develop symptoms due to hypercalcemia, that mostly include fatigue, malaise, constipation, bone and muscle pain, decreased concentration and depressive episodes [5, 28]. After obtaining laboratory blood examination results, we can observe increased levels of calcium and PTH that is indicative of hyperparathyroidism [6, 27]. Later we have to distinguish the cause of the disorder. Neck USG can be performed to identify if the gland is enlarged, although the results are usually not enough for diagnosis of hyperplasia [7, 8]. The Tc(99 m)-sestamibi scintigraphy can help with a diagnosis, by localization of changed parathyroid gland with a sensitivity of 70-90%, unfortunately its use is limited in multiple lesions of the gland, [9, 30]. Therefore, use of USG and scintigraphy could markedly increase sensitivity of the diagnosis. Unfortunately, recent studies showed that even this method is not very accurate and many patients cannot be diagnosed only upon the results of both of these examinations . APA are extremely rare and have only been described 23 times in literature [12, 27]. They lack specific criteria from histopathological point of view, it is not possible to differentiate them from benign adenomas and cancerous lesions neither by imaging methods nor macroscopically. Microscopically, they have some features of carcinoma - they adhere to contiguous structures, bends of fibrosis, solid trabecular growth, mitotic activity, but they do not invade the capsule, what is a hallmark of malignancy [12, 13, 26]. Although, the lack of specific criteria for histopathologic makes it extremely hard to always correctly diagnose the atypical adenoma (APA). The proposed criteria require the presence of at least 2 of those symptoms: intraoperative adherence, bands of fibrosis, pronounced trabecular growth, strong mitotic activity, necrosis, small cells with high nuclear/cytoplasmic ratio, cellular atypia in the absence of unequivocal signs of malignancy [13, 14, 24]. Use of imaging studies like USG or scintigraphy is limited, because it is not giving the definitive diagnosis. Clinical picture can be very varying, generally the hypercalcemia is slightly lower than seen in cancer, but higher than in typical adenoma (PA). All those similarities make it extremely difficult to distinguish atypical adenoma from carcinoma and benign lesion. The diagnosis of cancer should be supported if there is an invasion of capsule, vessels, neighbouring structures [14, 25]. The treatment of choice of atypical parathyroid adenoma (APA) is parathyroidectomy. Without evidence of macroscopic local invasion, the value of en bloc resection at initial surgery remains debatable. The surgeon performing the operation has to be very vigilant and check surrounding tissues for necrosis or any other abnormalities. Also helpful is intraoperative histopathological evaluation in case of doubt. After performing the procedure, the patient should be closely monitored, especially in unclear cases . From a histological point of view the parathyroid carcinoma (PC) can be misdiagnosed as an atypical adenoma (APA) - due to inadequate histopathological sample or other causes. Clinically, the physician should consider diagnosis of carcinoma when the patient presents with renal and bone symptoms simultaneously because dual presentation is quite rare in case of adenomas. Laboratory studies of very high levels of calcium and PTH also can indicate presence of malignancy. On physical examination and sonographic evaluation masses bigger than 3 cm should be considered to be malignant [17, 23]. Histopathological studies and genetic analysis of lesions can help with diagnosis of cancerous lesions, but are not always definitive. The diagnosis is confirmed if there is obvious sign of invasive growth of the tumor, either invasion of capsule, vessels, neighbouring structure or presence of metastasis at the time of presentation. Although metastatic progression of the tumor is very slow, usually cancer is in an earlier stage. Scintigraphy and USG studies are not very helpful because just upon them we cannot distinguish adenoma and carcinoma [15, 17]. Additionally, adjacent lymph nodes should be resected as well [16, 17]. If the diagnosis was confirmed based on the result of pathological studies of tumor resected during primary surgery, the treatment becomes more complex. Reoperation is advised in cases in which the surgery did not restore levels of calcium and PTH. In cases where primary surgery resolved the symptoms, patients should be strictly monitored and the levels of calcium and PTH should be measured regularly for surveillance of cancer return [17, 29]. Primary hyperparathyroidism is a clinical manifestation of benign and malignant conditions. Quick and precise diagnosis followed by surgical resection of hyperfunctioning tissue is the only curative approach [21, 22, 32]. Multidisciplinary approach should always be preferred in patients with this condition due to difficult differential diagnosis and not clear criteria .