(1) A few exceptional but serious cases have raised the possibility that hepatitis B vaccination could trigger or exacerbate demyelinating and autoimmune diseases. (2) Epidemiological data, i.e. three cohort studies and five case-control studies, showed no increased risk of demyelinating disease after hepatitis B vaccination. Another case-control study showed a significant link between multiple sclerosis and hepatitis B vaccination. Any increase in risk (if indeed there is one) probably affects only a small minority of vaccine recipients. But these few cannot be identified before vaccination. (3) Hepatitis B vaccination carries a very low risk of anaphylactic reactions (estimated incidence less than 1 case per 100 000 injections). (4) A few cases of haematological, rheumatological and autoimmune disturbance have been linked to hepatitis B vaccination. Appropriate epidemiological studies are needed to determine whether these links are causal. (5) In practice, hepatitis B vaccination has a favourable risk-benefit balance in non-immunised subjects who are at risk of contracting hepatitis B.