An 80-year-old man presented with a 6-month history of indurated tender purple papules. These had coalesced to form plaques with some central scarring and a dermatomal distribution on the left arm, immediately following herpes zoster (HZ) infection at this site. The patient had a 5-year history of small lymphocytic lymphoma (SLL), which was being managed conservatively under a 'watch and wait' protocol. On histological examination of a skin biopsy, marked interstitial granulomas and prominent granulomatous vasculitis were seen, supporting the clinical impression of a post-HZ granulomatous reaction. In addition, there was a dense monoclonal small B-cell lymphocytic infiltrate indicating koebnerization by SLL (a finding that has not been reported previously with concurrent postherpetic granulomatous vasculitis). Although benign pseudolymphomas occur in postherpetic cases, this case shows that even in association with benign vasculitic features true lymphomas can occur. Furthermore, this case highlights the importance of immunocytochemistry, molecular studies and clinicopathological correlation.