Prior studies examining the pharmacokinetics, safety, and efficacy of the new etonogestrel-containing single rod implantable contraceptive device, Implanon, did not include women who exceeded 130% of ideal body weight. Yet, as these women comprise a significant portion of the U.S. population, studies of Implanon in obese women are essential. The proposed study represents an important first step in addressing the lack of data on Implanon in obese women. We aim to examine the pharmacokinetics of Implanon in obese women during the first 6 months of use and to provide data on the acceptability, side effect profile, and ease of insertion, palpation, and removal in these women. We also aim to collect samples for future validation studies of the use of the blood spot (finger-stick blood sample on filter paper) as a method of determining plasma etonogestrel.