The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) can be induced by various conditions, including malignant neoplasms, infections, central nervous system disorders, and numerous drugs. We here report a case of a 65-year-old female patient, treated with quetiapine for schizophrenia, who presented with generalized tonic-clonic seizures and was finally diagnosed with quetiapine-induced SIADH. Quetiapine-associated hyponatremia is extremely uncommon and only a few, relevant reports can be found in the literature. This case underlines the fact that patients on antipsychotic medication and more specifically on quetiapine should be closely monitored and routinely tested for electrolyte disorders.