Costs were reported as discounted. The direct costs of HIV infections that could have been prevented by the implementation of a needle-exchange programme were calculated by multiplying the number of preventable HIV infections by the lifetime cost of treating an infection. The costs were discounted into present value. The quantities/costs boundary adopted was the hospital. The costs in terms of human suffering and loss were not included, nor, more importantly, were the costs associated with the programme factored into the analysis.