Tetany is a condition in which serum electrolyte disturbances lead to increased neuronal excitability. We describe a case of life-threatening tetany in a 2.5-year-old boy with Dent’s disease linked with the CLCN5 gene. Dent’s disease is a renal tubular disorder characterized by a proximal tubule defect resulting in low-weight proteinuria, hypercalciuria, phosphaturia, impaired urinary acidification, nephrolithiasis/nephrocalcinosis and progressive renal failure. In the presented patient, multiple electrolyte derangements in the form of hyponatremia, hypochloremia, hypokalemia, hypocalcemia, and hypomagnesemia, determined by Dent’s disease, led to the development of diffuse muscle spasm and rhabdomyolysis, which ended with acute hyperthermia and seizures. Although, due to acuity of symptoms sepsis was suspected, the child showed dramatic improvement after the aggressive electrolyte repletion. We emphasize the need for considering tetany in patients with unstable vital signs, muscle cramping and medical conditions underlying electrolyte disorders.