OBJECTIVE: Emergency patients with hypoalbuminemia are known to have increased mortality. No previous studies have, however, assessed the predictive value of low albumin on mortality in unselected acutely admitted medical patients. We aimed at assessing the predictive power of hypoalbuminemia on 30-day all-cause mortality in a cohort of acutely admitted medical patients. METHODS: We included all acutely admitted adult medical patients from the medical admission unit at a regional teaching hospital in Denmark. Data on mortality was extracted from the Danish Civil Register to ensure complete follow-up. Patients were divided into three groups according to their plasma albumin levels (0-34, 35-44 and ≥45 g/L) and mortality was identified for each group using Kaplan-Meier survival plot. Discriminatory power (ability to discriminate patients at increased risk of mortality) and calibration (precision of predictions) for hypoalbuminemia was determined. RESULTS: We included 5,894 patients and albumin was available in 5,451 (92.5%). A total of 332 (5.6%) patients died within 30 days of admission. Median plasma albumin was 40 g/L (IQR 37-43). Crude 30-day mortality in patients with low albumin was 16.3% compared to 4.3% among patients with normal albumin (p<0.0001). Patients with low albumin were older and admitted for a longer period of time than patients with a normal albumin, while patients with high albumin had a lower 30-day mortality, were younger and were admitted for a shorter period. Multivariable logistic regression analyses confirmed the association of hypoalbuminemia with mortality (OR: 1.95 (95% CI: 1.31-2.90)). Discriminatory power was good (AUROC 0.73 (95% CI, 0.70-0.77)) and calibration acceptable. CONCLUSION: We found hypoalbuminemia to be associated with 30-day all-cause mortality in acutely admitted medical patients. Used as predictive tool for mortality, plasma albumin had acceptable discriminatory power and good calibration.