Flare in disease activity occurred in four out of 73 patients (5%) under the age of 45 with systemic lupus erythematosus (SLE) who were immunized against poliomyelitis in a nationwide campaign following the Israeli outbreak of 1988. The flare appeared within 3 months of the immunization, whereas in 37 matched SLE patients who were not immunized, the disease remained stable in the same period. Both oral live-attenuated (OPV) and injected killed poliovaccines (IPV) were implicated in the flares (1/24 and 3/49 patients, respectively). The study was based on detailed questionnaires and confirmed by telephone calls and examination of the patients' hospital medical records. Poliovaccines, including IPV, should not be administered to SLE patients without careful consideration and a further prospective study should be undertaken to determine their safety in SLE.