BACKGROUND: Patients with malignancy comprise a unique group for whom transfusions play an important role. Because the need for transfusions may span a long period of time, these patients may be at risk for more adverse events due to transfusion than other patient groups. METHODS: A literature search on PubMed that included original studies and reviews was performed. The results were summarized and complemented by our clinical experience. Long-term complications of transfusions, such as transfusion-associated graft-vs-host disease, alloimmunization, transfusion-related immunomodulation, and iron overload, are discussed. RESULTS: Transfusion-related acute lung injury, transfusion-associated circulatory overload, and hemolytic transfusion reaction are deadly complications from transfusion. These adverse events have nonspecific presentations and may be missed or confused with a patient's underlying condition. Thus, a high level of suspicion and close monitoring of the patient during and following the transfusion is imperative. Common reactions (eg, febrile nonhemolytic transfusion reaction, allergic reaction) are not life threatening, but they may cause discomfort and blood product wastage. CONCLUSIONS: Every transfusion carries risks of immediate and delayed adverse events. Therefore, oncologists should prescribe transfusion for patients with cancer only when absolutely necessary.