This paper reports the results of a 'cost-of-illness' study of the socio-economic costs of back pain in the UK. It estimates the direct health care cost of back pain in 1998 to be pound1632 million. Approximately 35% of this cost relates to services provided in the private sector and thus is most likely paid for directly by patients and their families. With respect to the distribution of cost across different providers, 37% relates to care provided by physiotherapists and allied specialists, 31% is incurred in the hospital sector, 14% relates to primary care, 7% to medication, 6% to community care and 5% to radiology and imaging used for investigation purposes. However, the direct cost of back pain is insignificant compared to the cost of informal care and the production losses related to it, which total pound10668 million. Overall, back pain is one of the most costly conditions for which an economic analysis has been carried out in the UK and this is in line with findings in other countries. Further research is needed to establish the cost-effectiveness of alternative back pain treatments, so as to minimise cost and maximise the health benefit from the resources used in this area.