From six zones around Bahir Dar, the investigators will randomly select 60 districts. Half will be assigned randomly to start receiving iodized salt in July 2011; the other half will receive iodized salt as it becomes available in the market. From each district, 1-2 villages will be randomly selected for recruiting 30 children from each age group. It is assumed that with a pregnancy rate of 3.7%, approximately 166 children are born every year in a village of 4500, and 13 are born every month. So within 3 months, starting in May 2011, 30 children of each age could be recruited.