1. To evaluate effective and cognitive dysfunctions in subjects with a marginal form of thyroid hypofunction the authors studied a population of female goiter patients, divided in two groups on the basis of thyroid function: euthyroidism and subclinical hypothyroidism (SCH). 2. The SCH patients were treated with levothyroxine (LT4) in order to obtain euthyroidism, as demonstrated by normalization of the hormonal pattern. 3. Both groups were evaluated with a wide range of psychometric tests (Wechsler memory test, scribble test, reaction times) and psychopathological rating scales (Hamilton rating scales for depression and anxiety, brief psychiatric rating scale) at admission and after 3 months. 4. At admission, a significant decrease in logical memory was found in SCH patients; no differences in affectivity ratings were found between the groups. 5. After LT4 treatment, SCH patients showed a significant improvement in some items of memory performance. 6. In conclusion, when interfering factors relating to the perception of disease were excluded by employing euthyroid goiter patients as a comparison group, SCH appeared associated only with memory impairment, while the impairment of affective functions described in previous studies comparing SCH patients with normal controls was not confirmed. A significant improvement of memory skills was induced by LT4 treatment in SCH patients.