This study examined whether a mild elevation in serum Thyroid Stimulating Hormone (TSH) in normal older individuals was associated with a cognitive impairment. Participants consisted of 15 individuals with a high-TSH level and 82 with a normal TSH. The high-TSH group performed significantly worse than the normal-TSH group of tests of immediate and delayed verbal recall and on the Mini-Mental State Exam. This decrement was not due to group differences in processing resources nor was it explained by comorbid cerebrovascular disease, depression or anticholinergic drug usage. These results suggest that undetected mild thyroid dysfunction may contribute to the cognitive decrements found in older adults.