Background. Isolated TSH increase - „subclinical hypothyreosis“ (SH) appears to be comparatively common. Its incidence among women over sixty has been estimated up to 17 %. Though SH was assumed to be entirely asymptomatic, recent findings revealed various fine subjective and objective symptoms of the disease. Methods and Results. Twenty otherwise healthy female patients with SH diagnosis were examined. Using personality questionnaire MMPI/100 eight different clinical scales and two control scales were evaluated, using Wechsler’s memory scale WM-R 5 memory quotients were tested. The group was randomised i nto a subgroup treated for six month with placebo and a subgroup where thyroxin was administrated and thyroidal test normalised. Psychological testing repeated before and after the treatment, results evaluated using paired t-test. Results indicate that: 1. Patients with SH did not differ in personality features, they only had a higher tendency to the depressive mood, which could be positively influenced by thyroxin (significance at 5 % level). 2. Thyroxin treatment brought about improvement of some cognitive parameters of the verbal (p<0.01), visual (p<0.05), and general memory (p<0.01). 3. Results of psychological and cognitive tests correlate better with FT4 than TSH level. Conclusions. Though SH cannot be associated with changes in personality features, TSH normalisation results in statistically significant improvement of cognitive function - verbal, visual and general memory.

        Key words: subclinical hypothyreosis, neuro-psychological investigation, thyroxin treatment.