We describe a previously healthy woman who at the age of 44 years developed a factor VIII inhibitor, that over the years increased to a maximum level of 3600 Bethesda units (BU) mL(-1) in 1978. The epitope specificity of the factor VIII inhibitor was investigated and antibodies directed against the A2 and C2 domains of factor VIII were detected. The majority of these antibodies were of subclass IgG4. Over the years, the inhibitor titre gradually decreased and in 1989, the inhibitor could no longer be detected. Shortly after, the patient developed autoimmune haemolytic anaemia. A possible link between the disappearance of factor VIII inhibitors and the development of other autoantibodies may be explained by concomitant development of anti-idiotypic antibodies that neutralize the activity of factor VIII inhibitors. We were unable to detect anti-idiotypic antibodies, which could explain the decline in factor VIII inhibitor titre in this patient.