['We sought to compare the outcomes of in vitro fertilization (IVF) treatments in women with infertility-associated deep infiltrative endometriosis (DIE) who underwent extensive laparoscopic excision of endometriosis before IVF with those who underwent IVF only.', 'Prospective cohort study.', 'Infertility clinic and private hospital in São Paulo, Brazil.', 'A total of 179 infertile patients younger than 38 years had symptoms and/or signs of endometriosis and sonographic images suggestive of DIE.', 'After thorough counseling, 179 women were invited to participate in a prospective cohort study with 2 treatment options: IVF without undergoing laparoscopic surgery (group A, n = 105) and extensive laparoscopic excision of DIE before IVF (group B, n = 64). Ten women were lost to follow-up. The IVF outcomes were compared between the 2 groups.', 'In group B, patients had 5 +/- 2 (mean +/- SD) DIE lesions excised during laparoscopy. Patient characteristics in groups A and B, respectively, were: age (32 +/- 3 vs 32 +/- 3 years, p = .94), infertility duration (29 +/- 20 vs 27 +/- 17 months, p = .45), day-3 serum follicle-stimulating hormone levels (5.6 +/- 2.5 vs 5.9 +/- 2.5 IU/L, p = .50), and previous IVF attempts (1 +/- 1 vs 2 +/- 1, p = .01). The IVF outcomes differed between groups A and B, respectively, with regard to total dose of recombinant follicle-stimulating hormone required to accomplish ovulation induction (2380 +/- 911 vs 2542 +/- 1012 IU, p = .01), number of oocytes retrieved (10 +/- 5 vs 9 +/- 5, p = .04), and pregnancy rates (24% vs 41%, p = .004), but not number of embryos transferred (3 +/- 1 vs 3 +/- 1, p = 1). The odds ratio of achieving a pregnancy were 2.45 times greater in group B than in group A.'] Does extensive excision of deep infiltrative endometriosis before in vitro fertilization significantly improve pregnancy rates?