Despite recent advances in general supportive care, the mortality rate of patients with severe liver insufficiency remains high. Recently a new artificial liver support system MARS has been used for selective removal of albumin-bound toxins. Aim: To assess the safety and efficacy of MARS treatment in patients with acute on chronic liver disease (n = 5) or liver failure after extended hepatic resection (n = 1). Design/Patients: Six patients, aged 34-58 years, with severe liver insufficiency (mean MELD-score 31 (range 24-35)) were treated one to 16 times with the MARS system. At baseline three patients were intubated, three were encephalopathic (HE) and three had multifactorial kidney failure requiring kidney replacement therapy. Results and Conclusion: In all the patients MARS treatment significantly reduced the serum bilirubin levels. In three patients encephalopathy improved. In two patients the extracorporeal treatment precipitated a disseminated intravascular coagulation with clinically significant bleeding. Bridging to liver transplantation was possible in one patient, the other five patients died 30 days (2-74 days) after starting MARS therapy. Our case series shows that MARS treatment in general can be safely performed in patients with severe liver disease. However, in patients with an activated clotting system severe bleeding complication can be triggered and MARS treatment should be used very cautiously in these situations. MARS seems to be a promising new treatment option for patients with acute on chronic liver failure. However, carefully conducted randomized controlled trials are necessary to define its potential place in the treatment of patients with severe liver disease.