A 28-year-old woman, treated for schizophrenia, developed severe hypotonic hyponatremia (serum Na: 109 mEq/L) after several days of compulsive water drinking. The patient was admitted in a coma and required intensive supportive therapy. Rhabdomyolysis quickly followed with high serum creatine phosphokinase levels and myoglobinuria. A high volume alkaline diuresis was initiated. Renal failure or compartment syndrome did not complicate the clinical picture. The mechanisms causing water intoxication and hyponatremia are discussed as are the possible pathogenetic explanations behind acute hyponatremia and rhabdomyolysis.