Kasapoglu I, et al. - In this prospective, observational study, whether or not endometrioma is associated with a progressive decline in ovarian reserve was investigated, and the rate of decline was compared with the natural decline in ovarian reserve. All participants (40 women with endometrioma and 40 age-matched healthy controls) underwent serum antimüllerian hormone (AMH) testing twice, 6 months apart. Antral follicle count was also performed on sexually active patients with endometrioma. Observations revealed that compared to healthy women, women with an endometrioma experience faster progressive decline in serum AMH levels.