This cross-sectional prospective study assessed follicular-fluid anti-Mullerian hormone (AMH) concentrations in infertile patients with mild/minimal endometriosis during natural IVF. Thirty-two women participated in the study. Patients were divided into two groups: tubal obstruction without endometriosis (control group) and minimal/mild endometriosis (study group). All patients underwent laparoscopy for assessment of infertility; at the same time, any foci of endometriosis found were cauterized. AMH concentration was measured in the follicular fluid of a single follicle when it achieved pre-ovulatory maturation by ultrasensitive enzyme-linked immunosorbent assay. Likewise, AMH, FSH and inhibin B content in serum was also measured. Age (30±1.3 and 32±0.8years) and body mass index (22±0.6 and 22±0.5kg/m 2 ), day-3 antral follicle count (11.3±1.7 and 10.7±1.5), serum FSH concentrations (5.4±0.6 and 5.0±0.3IU/ml) and follicular-fluid AMH concentrations (1.8±0.3 and 1.5±0.1ng/ml, study and control group, respectively; mean difference 0.33, 95% CI −0.21 to 0.88) were similar in both groups. This study shows that infertile patients with minimal/mild endometriosis have a similar concentration of AMH in the follicular fluid after natural IVF as compared with control subjects. The purpose of this prospective study was to assess the follicular-fluid environment measuring anti-Mullerian hormone in infertile patients with mild/minimal endometriosis, which is a disease in which endometrial uterine tissue invades sites outside the uterus, during natural IVF. Measurement of anti-Mullerian hormone was chosen as it controls the formation of primary follicles and, therefore, has a role in folliculogenesis. Thirty-two women submitting to natural IVF cycles participated from the study. Patients were divided into two groups: tubal obstruction without endometriosis (control group), and minimal/mild endometriosis (study group). All patients underwent laparoscopy for assessment of infertility; at the same time, any foci of endometriosis found were cauterized. Anti-Mullerian hormone concentration was measured in the follicular fluid of a single follicle when it achieved pre-ovulatory maturation. Likewise, anti-Mullerian hormone content in serum was also measured, as well as FSH and inhibin B. Average age, approximately 30 years, was not statistically different between groups. In addition, day-3 antral follicular count (resting follicles at the beginning of each menstrual cycle), and serum FSH concentrations were also not statistically different between groups. Moreover, follicular-fluid AMH concentrations were also similar in both groups. This study shows that infertile patients with minimal/mild endometriosis have a similar concentration of AMH in the follicular fluid as compared with control subjects.