Background: Major abdominal surgery in older and frail patients is associated with considerable morbidity and mortality. Plasma albumin is routinely measured in the clinic and has been proposed as an indicator of frailty. This study aimed to investigate if plasma albumin is a predictor of mortality in older patients undergoing open abdominal surgery. Materials and methods: We conducted a single-center, register-based retrospective study of patients, aged ⩾60 years who underwent one of 81 open abdominal surgical procedures. Patients operated on during the period from January 1^st, 2000 to May 31^st, 2013 were consecutively identified in the Danish National Patient Registry. Plasma albumin was measured within 30 days prior to surgery and the primary endpoint was 30-day postoperative mortality. Results: 3,639 patients were included of whom 68.2% underwent emergency surgery. The rate of severe hypoalbuminemia (plasma albumin < 28 g/L) was 43.4%. Preoperative plasma albumin was lower in patients with a fatal 30-day outcome (mean 20.6 g/L vs 30.1 g/L in survivors, p < 0.0001). Other independent predictive parameters of 30-day mortality were age, male sex, and emergency surgery. We present an algorithm including these four variables for the prediction of 30-day mortality for patients aged ⩾60 years undergoing open abdominal surgery. Conclusion: Preoperative plasma albumin is a predictor of 30-day mortality in patients above 60 years of age following open abdominal surgery. Assessment of plasma albumin in conjunction with other risk factors such as age, sex, and surgical priority may improve preoperative decision-making.