Serious adverse effects of immunizations are uncommon. The hepatitis B vaccine has been implicated in a few dozen cases of extraarticular, systemic, or inflammatory joint disorders. We report two cases in which hepatitis A vaccination (Havrix, Smith Kline Beecham) was followed by a connective tissue disorder or a spondylarthropathy in two healthy males aged 50 and 24 years, respectively. Both patients were HLA B27-negative but carried the HLA DR1 and/or DR4 antigen. The outcome was favorable after treatment with a corticosteroid or a nonsteroidal antiinflammatory agent. The pathophysiology of immunization-related rheumatic disorders may involve circulating immune complexes and/or a mechanism similar to that seen in reactive arthritis, i.e., a genetically-determined susceptibility to the bacterial or viral antigens contained in vaccines.