Iodine is an important constituent for the synthesis of thyroid hormone. Deficient or excessive iodine intake may affect thyroid size and function.1 The strategy of Universal Salt Iodination (USI) has been implemented in China since 1996. The median urinary iodine (MUI) was 330 μg/L in 1997, and 306 μg/L in 1999. We conducted a cross-sectional epidemiological study in three counties (rural communities) in 1999 to investigate the effect of iodine intake on the prevalence of hypothyroidism.