Endocrine disorders have been frequently linked to recurrent pregnancy loss (RPL). Because embryo attachment and early implantation are exquisitely controlled by the local hormonal milieu, endocrine-related pregnancy failures are likely to occur early in gestation. Thyroid disorders, luteal phase defects, and polycystic ovary syndrome are the endocrine abnormalities most commonly associated with RPL. In this review we discuss new concepts in the pathophysiology and treatment of these diseases with the ultimate goal of improving pregnancy maintenance. We have also included our recommendations on testing and treatment of women with isolated and repeated pregnancy failure that is believed to be at least partially mediated by newly defined hypothyroidism, thyroid autoimmunity, luteal phase defects, obesity, and polycystic ovary syndrome.