Currently, primary hyperparathyroidism is the third most common endocrine disorder worldwide. In the last years, though, the numbers of patients with this diagnosis have been clearly increasing. Females are affected more often, and the age of patients is usually over 50 years. The diagnosis is guided by clinical symptoms of the patient and by biochemical and imaging methods results. [1] When parathyroid adenoma is identified as the source of primary hyperparathyroidism, the necessary extent of resection is performed. The present case involved a rapid diagnostic process necessary to stabilize the patient, together with localization of the adenoma for the indicated surgery. Ultrasound-guided exploration found a surprisingly large tumour of the parathyroid gland causing the acute clinical condition with symptoms suggestive of primary hyperparathyroidism with discrete mechanical compression of the upper mediastinum.Key words: critical diagnosis of hyperparathyroidism acute-active parathyroid adenoma extirpation of a huge parathyroid tumour - normalization of the clinical condition.