Overlap syndrome with systemic lupus erythematosus (SLE) and granulomatous polyangiitis with antineutrophil cytoplasmic antibody (ANCA) is rare. There are no international guidelines or randomised controlled trials for management. We present a woman in her 50s of Indian origin with a longstanding history of SLE who presented with new onset haematuria, rapidly declining kidney function and new proteinase-3-ANCA diagnosis. Biopsy findings were consistent with both lupus nephritis (LN) and ANCA-associated vasculitis (AAV)—predominantly ANCA vasculitis given the necrotising and crescentic features on histopathology. She was pulsed with methylprednisolone and subsequently managed with six cycles of low-dose intravenous cyclophosphamide with improvement to her kidney function. Her admission was complicated by cytomegalovirus (CMV) associated perinasal ulcers and colitis, which was managed with antiviral therapy. AAV/LN overlap syndrome is uncommon. Interaction between ANCA and SLE is not well understood. Readers should read more about CMV and its associated complications. Routine testing for CMV in the form of serology should be considered for patients prior to starting immunosuppressive therapy.