Acquired autoimmunity syndromes occur after viral vaccinations. Molecular mimicry is involved in these phenomena as is the necessity for the presence of two chemically complimentary antigens and an immunologic adjuvant. The HLA pattern of the host is also an important factor. The example used to explain these phenomena is demyelinating disease that follows hepatitis B vaccination. The somatic antigen of the hepatitis B virus in the vaccine has chemical complimentarity with the Epstein-Barr virus antigen in the vaccine recipient. The Epstein-Barr virus shows molecular mimicry with human myelin. The immunologic adjuvant is either present in the vaccine or muramyl peptides in the individual who is vaccinated. Why more than one type of autoimmune disease occurs is explained by the fact that specific autoimmune T-cells have been shown to develop clones that attack multiple human tissues.