Objective: To examine the economic impact of a new implantable contraceptive, Implanon(R), in comparison with other available contraceptive methods. Design: This was a modelling study using cost data derived from national published sources and effectiveness data from either controlled clinical trials (Implanon(R)) or reports in the literature (other contraceptives). In the baseline analysis, Implanon(R) was compared with 2 long term reversible contraceptives, Norplant(R) and Mirena(R). Further analyses were then carried out comparing Implanon(R) with Depo-Provera(R) and with combined oral contraceptives. Setting: The study concentrated on the UK, but also made reference to several other European countries. Main outcome measures and results: The baseline analysis showed that all 3 long term reversible contraceptives produce very good rates of return, with Implanon(R) providing the best rate of return (both average and internal) of the 3 methods. The payback period for Implanon(R) was calculated as 146 days, compared with 339 and 368 days for Norplant(R) and Mirena(R), respectively. In terms of cost effectiveness, the cost per protected year for Implanon(R) was pound 95, compared with pound 146 and pound 168 for Norplant(R) and Mirena(R), respectively. In comparison with Depo-Provera(R) (an injectable contraceptive), Implanon(R) was both less costly and more effective, the cost per protected year for Depo-Provera(R) being pound 131. The threshold beyond which Implanon(R) delivers cost savings compared with combined oral contraceptives was at a failure rate of 4.9% for the combined pill. Conclusions: Reversible long term approaches to contraception provide an effective and efficient use of healthcare resources and generate an excellent return on public investment. Implanon(R) produces better rates of return than both Norplant(R) and Mirena(R), and is also more cost effective in terms of cost per pregnancy avoided and cost per protected year than Norplant(R), Mirena(R), Depo-Provera(R) and oral contraceptives.