In an attempt to establish the characteristics, circumstances leading to infection and development of polyarteritis nodosa (PN) related to hepatitis B virus (HBV), prognostic factors and outcome, and to define the most effective treatment, 66 patients observed between 1972 and 1989 were analyzed. Hepatitis was clinically present in 19/66 patients before PN. In most cases, PN occurred less than 6 months after infection. Clinical manifestations of PN were comparable to those observed in patients without HBV infection except for orchitis which was present in 13.6% and for pulmonary signs which were absent. Transaminases were normal in 38 cases for SGOT and 31 for SGPT and twice the normal range or more in the other cases. Antineutrophil cytoplasmic antibodies (ANCA) were tested in 22 patients and present in 2 (9%). Twenty-eight patients were treated with prednisone +/- oral cyclophosphamide +/- plasma exchanges. Thirty-eight patients were given a short-term treatment with prednisone followed by the association of vidarabine, 15 mg/kg bw/d for one week and 7.5 mg/kg bw/d for 2 weeks, and plasma exchanges: 14 sessions during the 3 weeks of vidarabine infusion, then tapered until stopping treatment after 2 to 3 months depending upon the clinical results obtained. The mean duration of follow-up was 50.3 +/- 46.1 months. At the end of follow-up, 13 of the 28 patients (46.4%) treated with steroids +/- cyclophosphamide +/- plasma exchanges died and 7/38 (18.4%) of those treated with vidarabine and plasma exchanges (p < 0.001) died. HBe/anti-HBe seroconversion was observed in 2 patients treated with prednisone +/- cyclophosphamide +/- plasma exchanges who were alive at the time of final analysis and in 16 patients receiving the other regimen. The outcome of patients treated with a few days of prednisone, vidarabine and plasma exchange was good and, therefore, we propose this protocol as the first viable treatment for polyarteritis nodosa related to HBV, surpassing the conventional treatment with steroids and cyclophosphamide, which stimulates viral replication.