The authors describe a 25-year-old male with systemic vasculitis fulfilling the American College of Rheumatology classification criteria for both granulomatosis with polyangiitis (Wegener's granulomatosis) and polyarteritis nodosa. The patient was diagnosed with granulomatosis with polyangiitis following a mediastinal biopsy which revealed necrotising granulomas of the large airways, a positive cytoplasmic antineutrophil cytoplasmic antibodies and high antiproteinase 3 antibody titre. He then developed acute right-sided abdominal and testicular pain as well as areas of hyperaesthesia and parasthesiae on both lower limbs. He was found to have focal crescentic glomerulonephritis and mononeuritis multiplex, in keeping with his diagnosis of granulomatosis with polyangiitis, as well as two areas of infarction in his right testicle and multiple aneurysms of his hepatic and right renal arteries, more typical of polyarteritis nodosa. His symptoms developed 6 weeks after hepatitis B vaccination, which may have played an aetiological role.