Background: Due to expansion of longevity, the proportion of elderly people with multimorbidity is increasing. Our aim was to identify risk factors for all-cause mortality in elderly multimorbid medical in-patients one year after acute hospitalization. Information regarding risk factors is important to support targeted care plans after discharge. Methods: Prospective cohort study of patients acutely admitted to a medical department in a Norwegian regional hospital. Eligible patients were community-dwelling, received home care services before hospitalization, were aged 75+, and suffered from two or more chronic conditions. Inclusion period was 1. April – 31. October 2012. Candidate variables were number of daily prescribed drugs, Cumulative Illness Rating Scale for Geriatrics score, delirium, body mass index (BMI), handgrip strength, Barthel Activities of Daily Living Index score, and the laboratory analyses haemoglobin (Hgb), sodium (Na) and estimated glomerular filtration rate (eGFR). Results: We included 227 patients; mean age 86 years, 59% women, 71% lived alone. During the year after hospitalization, 39% died. In the adjusted cox proportional hazards regression analysis, significant and independent risk factors were BMI (hazard ratio (HR) 0.93, 95% confidence interval (CI) 0.88-0.98 per kg/m2), Hgb (HR 0.87, 95% CI 0.76-0.98 per g/100 mL), Na (HR 0.94, 95% CI 0.90-0.99 per mmol/L) and eGFR < 60 mL/min/1.73 m2 (HR 1.82, 95% CI 1.07-3.08).Conclusions: In this cohort of multimorbid elderly internal medicine patients, low body mass, hyponatremia, impaired renal function and anaemia were identified as independent and significant risk factors for one-year mortality.