Background : Although hypoalbuminemia is common in patients with tsutsugamushi disease, acute rickettsial infectious disease, its impact on the severity of disease is not reported. Therefore, we studied the role of hypoalbumiemia as a marker of the severity of disease in patients with tsutsugamushi disease. Methods : We retrospectively reviewed clinical data of 95 patients with tsutsugamushi disease who were admitted between January 1994 and December 1999 at Uijongbu St. Mary's hospital. We compared clinical and laboratory findings, complications, and mortality between hypoalbuminemic group (serum albumin < 3.0 g/dL) and control (serum albumin ≥ 3.0 g/dL). Results : Of the total 95 patients, 50 patients (52.6%) had hypoalbuminemia. In hypoalbuminemic group, the incidence of hypotension was higher (20.0% vs 2.2%, p=0.006) and the duration of admission was longer (12.0±4.5 vs 8.8±2.7 days, p<0.001), compared to control. The degree of thrombocytopenia in hypoalbuminemic group was severer than that in control (84,000±46,000 vs 138,000±75,000/mm3, p<0.001). Hypoalbuminemic group showed higher incidence of interstitial pneumonia (64.0 vs 13.3%, p<0.001), hypoxia (40.0 vs 6.6%, p<0.001), metabolic acidosis (12.0 vs 0%, p=0.018), and acute renal failure (18.0 vs 4,4%, p=0.038), compared to control. Four patients who had hypoalbuminemia died due to septic shock and multiorgan failure. Conclusion : This study shows that hypoalbuminemia could be used as a marker of the severity of disease in patients with tsutsugamushi disease.(Korean J Med 59:516-521, 2000)