Cutaneous periarteritis nodosa (PAN) is a clinical feature characterized by chronic, benign course; its pathogenesis is unknown. In patients submitted to renal transplantation cutaneous PAN is a rare complication. We report a case of cutaneous PAN associated with the reappearance of hepatitis B antigen 16 years after kidney transplantation. A 44-year-old man underwent successful renal transplantation in June 1980. In December 1996 he presented multiple painful erythematous subcutaneous nodules on both legs. Skin lesion biopsy showed the presence of cutaneous PAN. Six months later laboratory data demonstrated the presence of HbsAg. HBeAg, HBcAb and detectable HBV-DNA serum by polymerase-chain-reaction (PCR) assay. Anti-HBs and anti-HBe proved negative. In July 1998 the laboratory tests showed an important increase of HBV-DNA (5.1 billion by Branched DNA), and so lamivudine (100 mg/day) was introduced. HBV-DNA became undetectable by PCR after 3 months of therapy. Seven months later a new skin biopsy was performed. The typical signs of PAN were no longer evident. As HBV infecion was demonstrated six months after the clinical appearance of the PAN, in a patient who was believed to be immune to the virus, it is possible that, in the early stages, the hepatitis B antigen title was methodologically indeterminable, but sufficient to form circulating immune complexes responsible for vasculitis primer. Lamivudine therapy resulted efficacious in favouring the regression of cutaneous PAN, but its long-term efficacy requires further evaluation as regards potential selection of drug resistant hepatitis B virus (HBV) mutants during treatment.