In addition to the clinical management of blood supplies, the UK National Blood Service (NBS) examines short-term supply and demand to predict any potential shortages in blood supplies. However, very little data are available on the medium- and long-term trends. This paper describes blood product use in a United Kingdom Hospital Trust in 1999 and combines it with donor information to project the effect of demographic changes on demand and supply over the next 25 years. Overall, 2801 (4%) inpatients received transfusions of blood products. The proportion of inpatients receiving blood products increased with age. Patients aged >70 years used 46% of the total blood product supply, whereas patients aged <30 years used 10%. The estimated total cost associated with blood product use was pound 2 million during 1999 (2001-2002 prices). The results show that within 20 years, demand for blood products is expected to increase by 20% relative to the supply. The estimates in this study are a valuable aid to better long-term planning of supplies. As there is a paucity of data concerning blood product use in UK hospitals and blood use varies greatly between hospitals, further studies are required to guide blood product use policy.