This paper describes a case series of over 200 unintended pregnancies associated with the etonogestrel implant, Implanon. These cases have been reported to the Australian Adverse Drug Reactions Advisory Committee during the first 3 years of marketing in this country. Of 218 cases included, 45 had insufficient data to assess the reason for contraceptive failure and 46 women were determined to have been already pregnant prior to Implanon insertion. Of the remaining 127 cases, the most common reason for unintended pregnancy was failure to insert the implant in 84 women. Other reasons included incorrect timing of insertion (19 cases), expulsion of Implanon (3 cases) and interaction with hepatic enzyme-inducing medicines (8 cases). The remaining 13 cases were classified as product/method failures once other reasons had been excluded. Using the 204,486 Implanon devices subsidized in this period to estimate the population exposed and the 218 pregnancies reported, the approximate failure rate in postmarketing use was 1 in 1000 insertions. These findings (and reports to medical indemnity insurers) have resulted in the development of guidelines and training for doctors inserting Implanon in Australia.