BACKGROUND: 1) To assess thyroid function in a group of women in the first trimester of pregnancy who reside in a geographic area of moderate iodine deficiency. 2) To assess the usefulness of early pregnancy screening. METHODS: The study population included 240 women in the first trimester of pregnancy residing in the same valley in the Appenine Mountains (Casentino, Tuscany) characterized by a known moderate iodine deficiency. TSH, FT3, FT4, urinary iodine level, and anti-thyroid peroxidase autoantibodies (anti-TPO antibodies) were added to the tests included in the regional prescription pad for the first blood draw and data on thyroid disease and the use of iodized salt was also recorded. RESULTS: Of the 240 women examined, 55 (23%) had a TSH value over 2.5 mUI/L (NV= 2.51-9.89). A urinary iodine level of under 150 mu g/L was found in 170 women (70%). The median urinary iodine level in women using iodized salt was 103 mu g/L, while that in women not using it was 110 mu g/L (not a significant statistical difference). None of the women included in the study were taking iodine-containing supplements. CONCLUSIONS: In an area of known moderate iodine deficiency 23% of the women presented TSH values over 2.5 mUI/L and 70% of the women presented urinary iodine deficiency in the first trimester of pregnancy. This makes the case for thyroid function screening and strengthening of iodine supplementation at the beginning of pregnancy.