Infertility is defined as the inability to conceive after one year of regular intercourse without contraception. The prevalence of infertility is estimated between 12 and 14% and remains stable in recent years. It thus represents a common condition, with important medical, economic and psychological implications. According to a standard protocol infertility evaluation usually identifies different causes, including, male infertility (30%), female infertility (35%), the combination of both (20%), and finally unexplained or "idiopathic" infertility (15%). Female causes of infertility comprise endometriosis, tubal damage and ovulatory dysfunction (OD). Thyroid dysfunction is a condition known to reduce the likelihood of pregnancy and to adversely affect pregnancy outcome. Data on the relationship between thyroid disorders and infertility remain scarce and the association with a particular cause of infertility has not thoroughly been analyzed. In a case-control study we have shown that the relative risk of positive TPO-Abs in infertility due to a female cause and in particular related to endometriosis is significantly increased. Thyroid dysfunction itself is a condition interfering with normal ovarian function and was more frequent in women with positive anti-TPO Abs. We therefore propose that a systematic screening of TSH, free T4 and TPO-Ab could be considered in all women with a female cause of infertility. Prospective follow-up of a cohort of infertile women undergoing assisted reproduction shows a significant increased risk of miscarriage in women with positive anti-TPO Abs compared to women without thyroid auto-immunity after clinical pregnancy is established by the ART procedure. The frequent association of the presence of anti-TPO-Abs and miscarriage is hypothetical explained by the fact that organ specific autoimmune diseases may be secondary to some basic cellular abnormality that directly affects pregnancy outcome. Alternatively, women with thyroid autoimmunity, may experience greater changes in free thyroxine levels during ART and subsequent pregnancy interfering with genital tract physiology and fetal development. Determining the presence of thyroid antibodies before ART procedure is thus useful in identifying women at risk for subsequent clinical miscarriage.