In this research we investigated some neuropsychological parameters in school-age children living in two areas in which mild iodine deficiency has been found in the past. In Study 1 no significant difference was found in cognitive (WISC-R Block Design test), visuo-motor (WISC-R Coding test modified) and fine distal movements tasks. On the other hand in a Simple Reaction Time task children living in iodine deficient area were significantly slower than controls. In Study 2 the same results were obtained in the group of children born before an extensive iodine prophylaxis program, but not in younger children born later. Our data show that exposure to mild iodine deficiency in fetal/neonatal life does not affect general cognitive performance but slows the speed of motor responses, which may be due to an impairment concerning neural transmission mechanisms.