Background: Large-scale screening for coeliac disease has suggested that the disease is more prevalent than anticipated. In the screening studies published, only a minor proportion of those with a positive result have undergone jejunal biopsy to confirm the diagnosis. Our aim was to search for previously undiagnosed patients with coeliac disease by means of antiendomysium antibodies, which are more specific for the disease than serum antigliadin antibodies, and to study jejunal histology in each with a positive titre. Methods: Serum from 1070 adults working at Helsinki University Central Hospital were screened for untreated coeliac disease with IgA antiendomysium antibodies. All adults with positive titres underwent jejunal biopsy for villous structure analysis and counting of CD3-positive cells and cells bearing the gamma/delta T-cell receptor. Results: Coeliac disease was confirmed in a jejunal biopsy specimen from 8 of the 11 subjects with positive antiendomysium titres-that is, a frequency of 1 in 130. Seven of these eight coeliac patients had had minor abdominal discomfort for years, and one patient had a diagnosis of hyperthyroidism. None of the patients had osteoporosis, four had low iron storages, but only two were anaemic; no other nutritional deficiencies were found. The three other adults had a positive antiendomysium titre but a normal villous structure. One of these three was regarded as a false-positive case (titre, 1 in 5). The two other subjects (titres, 1 in 400) had increased numbers of CD3-positive T cells and gamma/delta T-cell receptor-bearing cells, suggesting a predisposition for coeliac disease. Conclusions: Undiagnosed coeliac disease is common in the adult population in Finland; in this study the prevalence was 1 in 130. Screening for coeliac disease is recommended on minor suspicion.