The prevalence of thyroid antibodies, indicating an autoimmune thyroiditis, has been shown to be significantly increased in patients with autoimmune diseases. A 3-year prospective follow-up study of 42 patients with biopsy-confirmed glomerulonephritis is presented. Although the majority of patients had been treated with immunosuppressants, the prevalence of thyroid peroxidase antibodies was unchanged in both females and males, 47 and 15% respectively, at follow-up. Likewise, the prevalence of thyroglobulin antibodies was unaffected as was that of antinuclear antibodies (ANA) when analysing males and females together. However, for males there was a trend to higher prevalence for ANA at follow-up. On the other hand, the prevalence of antineutrophil cytoplasmic antibodies declined. Furthermore, thyroid antibodies were not restricted to membranous nephropathy, and notably found in 4 out of the 8 patients with vasculitis.