Obesity reduces fertility and the effectiveness of fertility treatments in women, in addition to increasing pregnancy complications and programming of childhood obesity. Since studies have suggested that weight loss and lifestyle management could improve the fertility of women with obesity, obesity management with lifestyle modification is recommended for these women. Objectives: To evaluate the impacts of a lifestyle program in women with obesity and infertility on: 1) fertility outcomes, and 2) anthropometric and lifestyle measures. Methods: Women with obesity and infertility consulting at the fertility clinic of an academic hospital were randomized to the lifestyle program group (LPG) or control group (CG). Women in the CG began usual fertility care directly. Those in the LPG received the lifestyle intervention alone, without fertility treatments, for the first 6 months, and then in association with fertility treatments, if not pregnant. The lifestyle intervention combined individual and group sessions with a nutritionist and a kinesiologist in order to support progressive and sustainable lifestyle modifications. Per-protocol analyses including women who completed at least 6 months of the trial, or became pregnant, are presented. The maximal duration of follow-up, and intervention in the LPG, was 18 months or the end of pregnancy. Proportions were compared using chi-squared tests and means, using Student’s t tests. Results: Among 130 randomized women, 108 completed at least 6 months of the study or became pregnant (83%, 51 LPG and 57 CG). In these women, the lifestyle program increased by 58% the pregnancy rate as compared to controls (60.8% vs 38.6%, p=0.021) and almost tripled the proportion of women who conceived spontaneously, without fertility treatments (33.3% vs 12.3%, p=0.009). The lifestyle program also increased the live birth rate by 39% (51.0% vs 36.8%), although this was not statistically significant (p=0.139). When comparing participants with measures at 6 months of follow-up or at first pregnancy visit if before 6 months (75%, 46 LPG; 51 CG), women in the LPG lost significantly more % of weight (-3.4 ± 4.5% vs -0.89 ± 3.7, p=0.003), waist circumference (-2.9 ± 4.3 cm vs -0.97 ± 4.4, p=0.036) and % of fat mass (-1.3 ± 2.1% vs -0.47 ± 1.3%, p=0.033) compared to the CG. They also improved significantly more their lifestyle habits than the CG (healthy eating index: +18.2 ± 13.7 points vs +5.3 ± 12.4, p<0.001; total leisure activity’s energy expenditure: +0.77 ± 1.63 kcal/kg/day vs +0.17 ± 1.26 kcal/kg/day, p=0.044). Conclusion: A lifestyle program targeting women with obesity seeking fertility treatments improves not only their anthropometry and lifestyle habits, but most importantly, their chances of conceiving, especially spontaneously, in comparison to standard fertility treatments alone. Such impact could significantly reduce the costs associated with fertility treatments. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.