OBJECTIVE : To investigate the effect of age, clinical condition, and thyroid function on the prevalence of thyroid autoantibody positivity in hospitalized chronic geriatric patients. DESIGN : A screening study of hospitalized chronic geriatric patients. PARTICIPANTS : 249 non‐selected, hospitalized, chronic geriatric patients more than 60 years of age and 81 20 to 40‐year‐old healthy persons. MEASUREMENTS : Thyrotropin (TSH); thyroxine (T 4 ) and free thyroxine (FT4); and triiodothyronine (T 3 ), thyroglobulin (Tg), antibodies against thyroid peroxidase (AbTPO) and antibodies against thyroglobulin (AbTg) estimation in a screening study. RESULTS : AbTPO positivity (AbTPO+) was found more often than AbTg positivity (AbTg+) (15.3% vs 9.2%, P = .04), one being positive (Ab+) in 19.3%. The occurrence was higher in females than males (Ab+:27.1% vs 7.1%, P < .001; AbTPO+:21.9% vs 5.1%, P < .001; AbTg+:13.2% vs 3.1%, P = .0052). Among the Ab+ patients, AbTPO was more often positive than AbTg (40/48 vs 21/48, P < .001). The sensitivity, specificity, and positive predictive value of Ab positivity to detect a thyroid disorder were 0.35, 0.85 and 0.38, respectively. Within the population of euthyroid geriatric patients, the occurrence of AbTg+ (χ 2 (2) = 8.65, P = .013) and Ab+ (χ 2 (2) = 8.02, P = .018) correlated positively with the age of the patients, and there was also a female predominance (AbTPO+ 18% vs 3.7% in the males; AbTg+ 13% vs 2.4%; Ab+ 25.8% vs 6.1%). When compared with 20 to 40‐year‐old subjects, only the euthyroid ≥ 80‐year‐old patients showed a significantly higher occurrence of Ab+ (26.2% vs 9.9% χ 2 (1) = 5.64, P = .017). In the euthyroid ≥80‐year‐old females, AbTPO+ was 25%, AbTg:22.2%, and Ab+: 36.1%!. The nonthyroidal clinical state of the euthyroid patients did not correlate with the antibody prevalence. CONCLUSIONS : In hospitalized chronic geriatric patients, AbTg and especially AbTPO positivity is frequent, even in euthyroid patients without goiter. This aspecific Ab positivity in the euthyroid state correlates to the age, but not to the severity of the nonthyroidal clinical condition of the patients and explains why the Ab positivity is not predictive enough for thyroid dysfunction in this subpopulation. Thus, in hospitalized chronic geriatric patients the AbTg and AbTPO titers should be examined only in cases where thyroid screening (TSH) reveals abnormal results.