Antineutrophil cytoplasmic antibodies (ANCA) are generally believed to be strongly associated with some primary systemic vasculitides (PSV), such as Wegener's granulomatosis (WG), microscopic polyangiitis (MPA), and Churg-Strauss syndrome (CSS), which have some clinical manifestations in common and are 'pauci-immune' by immunohistology. This group of PSV has thus been termed 'ANCA-associated vasculitis' (AAV). By contrast, essential mixed cryoglobulinaemic vasculitides (EMC) are clinically heterogeneous and characterized immunologically by complement consumption and by immunocomplex depositions; they are also characteristically ANCA-negative. We report here on two SV-patients in whom the detection of cANCA (proteinase 3-ANCA in one case) in conjunction with glomerulonephritis and various extrarenal vasculitic lesions was suggestive of an AAV. However, demonstration of type II cryoglobulinaemia in conjunction with hypocomplementaemia, and histological proof of immunocomplexes in the glomerulus led to the diagnosis of an EMC, which was associated with hepatitis C virus (HCV) infection in one of the cases. Against the setting of 'false positive' cANCA in EMC, we discuss the differential diagnostic steps as well as current differential therapeutic approaches.