BACKGROUND The objective of this study was to assess the effect of timing of postpartum levonorgestrel-releasing intrauterine device (IUD) insertion on breast-feeding continuation. METHODS Women interested in using a levonorgestrel IUD postpartum were randomized to immediate postplacental insertion (postplacental group) or insertion 6-8 weeks after vaginal delivery (delayed group). Duration and exclusivity of breast-feeding were assessed at 6-8 weeks, 3 months, and 6 months postpartum. Only women who received an IUD were included in this analysis. RESULTS Breast-feeding was initiated by 32 (64%) of 50 of women receiving a postplacental IUD and 27 (58.7%) of 46 of women receiving a delayed IUD (p=.59). More women in the delayed group compared with the postplacental group continued to breast-feed at 6-8 weeks (16/46 vs. 15/50, p=.62), 3 months (13/46 vs. 7/50, p=.13), and 6 months postpartum (11/46 vs. 3/50, p=.02). The results did not differ when only women who initiated breast-feeding or only primiparous women with no prior breast-feeding experience were analyzed. CONCLUSIONS Immediate postplacental insertion of the levonorgestrel IUD is associated with shorter duration of breast-feeding and less exclusive breast-feeding. Further studies on the effects of early initiation of progestin-only methods on women's lactation experience are needed.