here is limited data on the prevalence of thyroid dysfunction in the older population. This study aimed to determine the prevalence of thyroid dysfunction among a sample of Iranian older adults. A cross-sectional analysis of older adults who aged 60 years and over was conducted. A total of 363 subjects were randomly selected from Birjand longitudinal aging study (BLAS) cohort study. Serum thyroid-stimulating hormone (TSH) level, total thyroxine (T4) and total triiodothyronine (T3) were measured by the enzyme-linked immunosorbent assay (ELISA). Based on thyroid function tests and history of taking medicines used to treat thyroid disorders, participants were classified into the following groups: euthyroid, overt/subclinical hypothyroidism, and overt/subclinical hyperthyroidism. Subsequently, the crude and World Health Organization (WHO) age-standardized prevalence were estimated for different thyroid function categories. A total of 171 men and 192 women, aged 60-94 years, were randomly selected. The crude prevalence of total hypothyroidism was 22.31% (subclinical [18.46%], overt [3.86%]), and that of hyperthyroidism was 1.66% (subclinical [1.38%], overt [0.28%]). The crude prevalence of total thyroid dysfunction was, therefore, 23.97%. A female preponderance was noticed in both total (P-value = 0.035) and overt (P-value = 0.035) hypothyroidism. An increasing trend with age was noticed in the prevalence of total hypothyroidism (P-value = 0.049). Age-standardized prevalence of total hypothyroidism and hyperthyroidism was 26.63% (95% confidence interval [CI] 20.58-33.69%) and 1.11% (95% CI 0.49-2.51%), respectively. A considerable proportion of our study population demonstrated evidence of thyroid dysfunction, particularly subclinical hypothyroidism. Our findings highlight the importance of further investigation of thyroid disorders among older Iranian adults.