Coeliac disease was searched for in a series of 776 children with newly diagnosed IDDM. During the follow-up of 2 to 3 years from diagnosis, reticulin and gliadin antibodies were measured, and a jejunal biopsy was performed in those cases with high levels of antibodies; 19 children were identified with coeliac disease, giving the prevalence of 2.4%. In only one case had coeliac disease been diagnosed before IDDM. Nine patients with proven coeliac disease were negative for antibodies when IDDM was diagnosed, but became positive within 24 months. All patients found to have coeliac disease were positive for IgA reticulin antibodies, but only 12 of 18 (67%) showed a high level of IgA gliadin antibodies. Of the 18 patients genotyped for HLA DR locus, 14 (78%) were positive for DR3 and 10 (56%) were positive for DR4. DQB1*0201 allele was present in 17 of 18 patients (94%). Coeliac disease in children with IDDM tends to develop soon after diabetes is diagnosed. Routine screening for coeliac disease is recommended repeatedly during the first years after the diagnosis of IDDM.