Objective: Various studies have shown that a number of infectious disease causes syndrome of inappropriate antidiuretic hormone (SIADH). However, the relationship between infectious disease and SIADH is not yet fully known. In this prospective study, we aimed to assess the presence of SIADH in patients with brucellosis. Patients and methods: Thirty-five patients with acute brucellosis were retrospectively reviewed. The diagnosis of brucellosis was performed using the Wright test in connection with blood culture. SIADH was defined by euvolemic hyponatremia (serum sodium level lower than 135 mEq/l) with increased urinary sodium excretion (urinary sodium higher than 40 mmol/l). Results: Of the 35 patients, 19 (54%) had SIADH; 20 (57%) also had hypouricemia (uric acid level lower than 4 mg/dl). Additionally, all of the studied patients had a high mean urinary sodium excretion rate (mean 132 mmol/l; range 40-224). Most importantly, the hyponatremic patients were more likely to have a lower albumin level (P < 0.01). Conclusions: SIADH is a major complication of brucellosis. The presence of SIADH could be a diagnostic tool for diagnosing brucellosis. Further larger randomized studies may confirm these findings. (C) 2014 Wiley Periodicals, Inc.