Objective: To describe the relationship between clinical practice and national guidelines for the transfusion of red blood cells (RBCs), fresh frozen plasma (FFP), platelets, and cryoprecipitate in Australian and New Zealand intensive care units (ICUs). Setting: Forty-seven ICUs over a 5-week period from August to September 2008. Design: Prospective, observational, multicentre, cohort study. Patients: A total of 874 patients receiving any type of blood transfusion. Methods: All patients who were transfused at least one unit of any blood component were included. Patient-specific and blood-component specific data were gathered. Pre-transfusion haemoglobin, platelet count, international normalised ratio (INR), and fibrinogen levels were compared to national guidelines. Results: Of all 874 patients, 757 received RBCs (86.6%), 231 (26.4%) received platelets, 340 (38.9%) received FFP, and 78 (8.9%) received cryoprecipitate. Bleeding was the reason for administration of RBCs in 46%, FFP in 55%, and platelets in 47% of transfusions. The mean (SD) pre-transfusion haemoglobin was 77.6 (9.5) g/l, while the geometric means (95% CI) for platelet count, INR, and fibrinogen were 67.0 (59.7–75.3) × 109/l, 1.84 (1.76–1.93), and 1.4 (1.1–1.8) g/l, respectively. The proportions of transfusions not adherent to guidelines were 2% for RBC, but 53% for platelets, 29% for FFP, and 88% for cryoprecipitate (RBC vs. other transfusion p < 0.001 for all). Conclusions: Transfusion practice of RBCs in Australian and New Zealand ICUs is restrictive and is concordant with guidelines. However, the transfusion of other blood components is not.