Objectives. To evaluate the prevalence of infertility in women with Graves' disease (GD) or Hashimoto's thyroiditis (HT) and associated factors. Material and Methods. This cross-sectional study was conducted at the Endocrinology Clinic for Thyroid Autoimmune Diseases, with 193 women aged 18-50 years with GD and 66 women aged 18-60 years with HT. The women were interviewed to obtain data on their gynecological and obstetric history and family history of autoimmune diseases. Their medical records were reviewed to determine the characteristics of the disease and to confirm association with other autoimmune diseases. Infertility was defined as 12 months of unprotected sexual intercourse without conception. Results. The prevalence of infertility was 52.3% in GD and 47.0% in HT. Mean age at diagnosis was 36.5 years and 39.2 years, in GD and HT, respectively. The mean number of pregnancies was lower in women who were 35 years old or younger at diagnosis and was always lower following diagnosis of the disease, irrespective of age. The only variable associated with infertility was a shorter time of the disease in HT. Conclusions. The prevalence of infertility was high in women with GD and HT and affected the number of pregnancies in young women.