This paper examines first the economic costs and benefits of total hip replacement in Britain and, secondly, the general social and economic factors which may help to determine the future development of both new and established forms of joint replacement surgery. It estimates that there is a monetary benefit to cost ratio of at least ten to one associated with total hip replacement among people aged under 60 and one of at least two to one amongst individuals in the 60-70 age group. Overall, the N.H.S.s expenditure of up to Pound 15 million (maximum) on hip replacement surgery in 1974 will probably generate a total economic return to the community of at least Pound 60 million in 1974 terms. It is noted that joint replacement techniques can alleviate pain and handicap against which other forms of medical intervention are often of very limited value. However, significant risks are involved. The in-hospital mortality rate associated with total hip replacement is put at between 1 and 2% and the national average risk of failure, in terms of the operative outcome not being good or excellent, is estimated at marginally above 10%. For other joint replacement techniques such rates may be higher and the benefits conferred less desirable. It is suggested that the facilities available in this area of orthopaedic surgery are already carrying a maximum work load and that the N.H.S. may not be able to meet future increases in demand, given the very limited resources likely to be available for capital investment in the health services during the remainder of this decade. A lack of adequate knowledge of the social and economic impact of joint replacement techniques could exacerbate possible under-financing of or sub-optimal use of resources in this sector of medical care. It is pointed out there is a possibility that investment in more new specialist centres for orthopaedic surgery could help to reduce or keep to a minimum the hazards inevitably associated with joint replacement.