IgA nephropathy is the most frequent primary glomerulonephritis worldwide. At its onset, the most common laboratory sign is isolated haematuria often accompanied with mild proteinuria (up to 1.5 g/24 h). The disease displays a progressive course with end-stage renal disease occurring in up to half of patients 20 years after onset. Diagnosis is established by immunofluorescent microscopy of a renal biopsy specimen. Discoveries in the past decade on the pathogenesis of IgA nephropathy together with complex evaluation of its clinical presentation enable to establish diagnosis with a satisfactory degree of probability even without biopsy. IgA nephropathy patients display increased or borderline serum IgA levels; increased serum levels of IgA fraction with degalactosylated O-linked side sugar chains; increased serum levels of anti-N-acetylgalactosamine antibodies; increased levels of circulating immune complexes composed of IgA1 complexed with IgG or IgA1; increased serum levels of circulating complexes composed of IgA and fibronectin; and frequent occurrence of the rheumatoid IgA factor. Clinical use of these still generally unavailable methods would reduce the renal biopsy indication in patients with isolated or predominant haematuria.