Key Clinical MessageSoporous state in acute renal failure represent an atypical presentation of parathyroid cancer. Complete prompt investigations and diagnosis have a fundamental role in the management of this diseaseAbstractThis report describes a case of parathyroid carcinoma (PC) with an uncommon first clinical presentation: soporous state, depression, and severe cognitive decline in association with acute renal failure. After discovering extremely high serum calcium and parathyroid hormone (PTH) levels, the diagnosis of primary hyperparathyroidism (pHPT) was made and a surgical en bloc resection was performed. After the surgical intervention, the histological examination revealed the presence of a malignant parathyroid disease, thus confirming our first preoperative suspicion.