A prospective survey for thyroid disease in 317 consecutive patients admitted to a Geriatric Unit is described, in which protein bound iodine (P.B.I.) and triiodothyronine (T3) uptake estimations were the initial tests of thyroid function. The overall prevalence of thyroid disease was 5·7 per cent. In view of the poor correlation between clinical assessment and thyroid function in the elderly patients in this series, routine use of thyroid function tests is recommended to detect the substantial number of elderly patients with untreated and unrecognized thyroid disease.