Partial liver resections are the treatment of choice for patients with a malignant liver or bile duct tumor. The most frequent indications for partial liver resections are colorectal metastasis, hepatocellular carcinoma (HCC) and cholangiocarcinoma. Liver resection is the only therapy with a chance for cure in these patients. Refinements in surgical technique and increasing experience have contributed to a reduction in perioperative morbidity and mortality in recent years. Despite these improvements, partial liver resections remain a major surgical procedure and carry the risk for excessive blood loss and a subsequent need for blood transfusion. Blood transfusions have been associated with systemic side effects, such as depression of the immune system. Several studies have suggested that perioperative blood loss or transfusions have a negative impact on postoperative outcome. However, it has been debated whether this is due to a real cause-effect relationship or merely the result of more complicated surgery. We have reviewed the literature concerning studies focusing on the relationship between blood loss and blood transfusion during liver surgery for malignant tumors and postoperative outcome. Most studies were based on a retrospective analysis of single center experiences, using uni- and multivariate statistical methods. Most studies have demonstrated a significant and clinically relevant association between blood transfusion and postoperative mortality and morbidity, especially postoperative infectious complications. The effect of blood transfusions on tumor recurrence and more long-term mortality is much less clear and evidence varies depending on the type of malignancy. The strongest indication that blood transfusion may have an impact on tumor recurrence has been found for patients with early stages of HCC. However, overall, no such effect could be demonstrated for patients undergoing partial liver resection for late stages of HCC, colorectal liver metastasis or cholangiocarcinoma.