General practitioners are increasingly expected to screen elderly patients for common disorders, such as hypothyroidism, and the identification of at-risk patients by simple means would reduce the financial and other costs of such screening. A general practice based study of 1193 patients aged 60 years and over has been carried out to investigate the usefulness of the following factors in identifying those in whom biochemical testing for hypothyroidism would be indicated: personal history or family history of thyroid disease, symptoms of thyroid disease and body mass index. Of the 190 patients with either a personal or family history of thyroid disease, 28 (14.7%) had an elevated concentration of thyroid-stimulating hormone. Thus, 66 of the 94 patients (70.2%) with elevated concentrations of thyroid-stimulating hormone had no such thyroid history. Similarly, only nine (4.7%) of the patients with a personal or family history of thyroid disease required thyroxine replacement therapy. Thus, 22 of the 31 patients (71.0%) requiring such treatment had no such history. Discriminant analysis of the responses of women patients to questions concerning personal or family history of thyroid disease, the presence of symptoms of hypothyroidism, their age and body mass index identified only 51.3% of those with an elevated thyroid-stimulating hormone concentration and 77.2% of those with normal thyroid-stimulating hormone. Analysis of the responses of the men patients was even less discriminating.(ABSTRACT TRUNCATED AT 250 WORDS)