The hypothesis was tested that thyroid function, as indicated by serum thyroid-stimulating hormone (TSH) Level, is associated with cognitive performance in a healthy aging population. In a random sample of 120 participants recruited from the Maastricht Aging Study (MAAS), aged between 49 and 71 years, we assessed TSH Level, mood state (Symptom Check List, subscale depression), and three domains of cognitive function: verbal memory, general sensorimotor speed, and complex flexibility. After correction for age, sex, and educational level, a negative association between TSH and memory function was apparent: higher levels of TSH predicted Lower levels of memory performance. Exclusion of individuals with TSH levels suspect for thyroid disorder (n = 2) or who were on thyroid relpacement (n = 3) attenuated this association. Furthermore, additional control for mood status reduced the association below the significance level. No interaction between age and TSH on cognition was found, which indicated that the TSH-memory association was independent of age group Level. We conclude that the association between TSH level and memory performance was small and dependent on mood status and the presence of (possible) thyroid disease in this relatively healthy population based sample. Prospective studies are needed to address the rote of thyroid function in age-related cognitive decline.