Hypercalcemic crisis (HC) is a rare and severe complication of primary hyperparathyroidism (PHPT), characterized by markedly elevated serum calcium levels and diverse clinical manifestations. PHPT is the primary cause of hypercalcemia and is often asymptomatic. The factors that trigger HC in PHPT are not fully understood. Here we report a patient who was diagnosed with HC resulting from previously undetected PHPT. Remarkably, the patient exhibited no symptoms of PHPT before the HC episode. The patient presented with neurological symptoms, including altered behavior and slurred speech, which were attributed to hypercalcemia. The probable trigger for HC in this case appears to be an acute febrile illness related to a urinary tract infection (UTI). The occurrence of an acute febrile illness or UTI as a precipitating factor for HC in PHPT is a rare and infrequently documented phenomenon in the existing medical literature.