The introduction of anti-tumour necrosis factor (TNF) agents for the treatment of rheumatoid arthritis (RA), Crohn's disease (CD) or spondyloarthritis (SpA) has revolutionised the therapeutic approach to patients with active disease failing to respond to conventional therapy. However, some of the patients treated with selective TNF inhibitors may develop autoantibodies, such as antinuclear antibodies (ANAs) and anti-double-stranded DNA (anti-dsDNA) antibodies. Furthermore, anti-phospholipid antibodies, which are mainly detected by means of anti-cardiolipin assays, have been found in RA patients receiving TNF blockers. There have also been a number of reports of the development of anti-drug antibodies, of which those against infliximab can interfere with the drug's pharmacokinetics (and therefore its effects), and may also cause acute and delayed infusion and injection site reactions. The onset of autoimmune diseases during biological treatment is rare, but it needs to be promptly recognised in order to plan appropriate patient management. The addition of an immunosuppressive drug can reduce the induction of anti-TNF antibodies.